<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019fd749-6588-78a8-af51-c5f146b7df2f,g:328341ce-1bb1-4d13-b697-5c1676710ff5-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.oldnational.com/role/Cover" xlink:type="simple" xlink:href="onb-20260930.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019fd749-6a2e-7954-a23a-7799b458332a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntitiesTable_019fd749-6a2e-7954-a23a-7799b458332a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fd749-6a2e-7db2-a190-3a051d08fa36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019fd749-6a2e-7954-a23a-7799b458332a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fd749-6a2e-7db2-a190-3a051d08fa36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd749-6a2e-7db2-a190-3a051d08fa36_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd749-6a2e-7db2-a190-3a051d08fa36" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd749-6a2e-7db2-a190-3a051d08fa36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fd749-6a2e-790b-95dd-f36e610a9bd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019fd749-6a2e-7db2-a190-3a051d08fa36" xlink:to="loc_us-gaap_ClassOfStockDomain_019fd749-6a2e-790b-95dd-f36e610a9bd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fd749-6a2e-7725-939e-f0ba0921106d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd749-6a2e-790b-95dd-f36e610a9bd2" xlink:to="loc_us-gaap_CommonStockMember_019fd749-6a2e-7725-939e-f0ba0921106d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DepositarySharesEachRepresentingA140thInterestInAShareOfNonCumulativePerpetualPreferredStockSeriesAMember_019fd749-6a2e-7ef6-bc63-fa46d1011109" xlink:href="onb-20260930.xsd#onb_DepositarySharesEachRepresentingA140thInterestInAShareOfNonCumulativePerpetualPreferredStockSeriesAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd749-6a2e-790b-95dd-f36e610a9bd2" xlink:to="loc_onb_DepositarySharesEachRepresentingA140thInterestInAShareOfNonCumulativePerpetualPreferredStockSeriesAMember_019fd749-6a2e-7ef6-bc63-fa46d1011109" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DepositarySharesEachRepresentingA140thInterestInAShareOfNonCumulativePerpetualPreferredStockSeriesCMember_019fd749-6a2e-7f5a-9af9-f20deb4107d6" xlink:href="onb-20260930.xsd#onb_DepositarySharesEachRepresentingA140thInterestInAShareOfNonCumulativePerpetualPreferredStockSeriesCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fd749-6a2e-790b-95dd-f36e610a9bd2" xlink:to="loc_onb_DepositarySharesEachRepresentingA140thInterestInAShareOfNonCumulativePerpetualPreferredStockSeriesCMember_019fd749-6a2e-7f5a-9af9-f20deb4107d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019fd749-6a2e-7a9d-8929-037f9df635e0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_DocumentType_019fd749-6a2e-7a9d-8929-037f9df635e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019fd749-6a2e-7085-9604-ad2f93ab2a8d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_DocumentQuarterlyReport_019fd749-6a2e-7085-9604-ad2f93ab2a8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019fd749-6a2e-7b4e-8e01-f02548c3b76b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_DocumentPeriodEndDate_019fd749-6a2e-7b4e-8e01-f02548c3b76b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019fd749-6a2e-7418-b60c-c67521876254" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_DocumentTransitionReport_019fd749-6a2e-7418-b60c-c67521876254" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019fd749-6a2e-72f2-b9de-04307a3c6e14" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityFileNumber_019fd749-6a2e-72f2-b9de-04307a3c6e14" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019fd749-6a2e-76a4-80e7-60f83b9602ee" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityRegistrantName_019fd749-6a2e-76a4-80e7-60f83b9602ee" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019fd749-6a2e-79f1-9a3a-c662777eaced" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019fd749-6a2e-79f1-9a3a-c662777eaced" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019fd749-6a2e-736f-b980-5b2329c8b7bc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityTaxIdentificationNumber_019fd749-6a2e-736f-b980-5b2329c8b7bc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019fd749-6a2e-7ab4-a632-548bcca31742" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityAddressAddressLine1_019fd749-6a2e-7ab4-a632-548bcca31742" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019fd749-6a2e-7e58-9c86-cea4f779f6b0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityAddressCityOrTown_019fd749-6a2e-7e58-9c86-cea4f779f6b0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019fd749-6a2e-7850-bcda-82b21d8c2432" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityAddressStateOrProvince_019fd749-6a2e-7850-bcda-82b21d8c2432" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019fd749-6a2e-7e96-a264-1863aaccf9e6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityAddressPostalZipCode_019fd749-6a2e-7e96-a264-1863aaccf9e6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019fd749-6a2e-77ed-a038-1c98961a986d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_CityAreaCode_019fd749-6a2e-77ed-a038-1c98961a986d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019fd749-6a2e-7f4e-80c9-57291523eacc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_LocalPhoneNumber_019fd749-6a2e-7f4e-80c9-57291523eacc" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019fd749-6a2e-7535-835a-68a53e048b6f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_Security12bTitle_019fd749-6a2e-7535-835a-68a53e048b6f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019fd749-6a2e-78e4-8c53-4286133a274a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_TradingSymbol_019fd749-6a2e-78e4-8c53-4286133a274a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019fd749-6a2e-770d-8e12-c6bf243f6a99" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_SecurityExchangeName_019fd749-6a2e-770d-8e12-c6bf243f6a99" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019fd749-6a2e-74b7-91ab-726894aa4662" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityCurrentReportingStatus_019fd749-6a2e-74b7-91ab-726894aa4662" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019fd749-6a2e-7e25-b794-ce18bcc60d7f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityInteractiveDataCurrent_019fd749-6a2e-7e25-b794-ce18bcc60d7f" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019fd749-6a2e-7ae3-ac9c-cb94ab597c7b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityFilerCategory_019fd749-6a2e-7ae3-ac9c-cb94ab597c7b" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019fd749-6a2e-7fb2-b39f-f81eaf3d7ab8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntitySmallBusiness_019fd749-6a2e-7fb2-b39f-f81eaf3d7ab8" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019fd749-6a2e-7cc8-acee-4e0e73922661" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityEmergingGrowthCompany_019fd749-6a2e-7cc8-acee-4e0e73922661" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019fd749-6a2e-720a-9fc6-67c84ac0c91d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityShellCompany_019fd749-6a2e-720a-9fc6-67c84ac0c91d" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019fd749-6a2e-79ab-a48b-15f1e6bde820" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019fd749-6a2e-79ab-a48b-15f1e6bde820" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019fd749-6a2e-77d8-afc8-6a444091d6ff" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_AmendmentFlag_019fd749-6a2e-77d8-afc8-6a444091d6ff" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019fd749-6a2e-78e5-9944-5807027eb080" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_DocumentFiscalYearFocus_019fd749-6a2e-78e5-9944-5807027eb080" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019fd749-6a2e-77c7-919f-0a92512c1253" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019fd749-6a2e-77c7-919f-0a92512c1253" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019fd749-6a2e-79b5-a8c2-c6f725ca3381" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_EntityCentralIndexKey_019fd749-6a2e-79b5-a8c2-c6f725ca3381" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019fd749-6a2e-7351-a00a-e676e25e24e0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019fd749-6a2e-7983-8448-96f2987210f9" xlink:to="loc_dei_CurrentFiscalYearEndDate_019fd749-6a2e-7351-a00a-e676e25e24e0" xlink:type="arc" order="28"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/CONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="onb-20260930.xsd#CONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/CONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fd749-6a2e-7b10-b2e5-c626ac34b024" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019fd749-6a2e-73e1-8725-292e71c177f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019fd749-6a2e-7b10-b2e5-c626ac34b024" xlink:to="loc_us-gaap_StatementTable_019fd749-6a2e-73e1-8725-292e71c177f8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6a2e-7362-ab59-55eaa3238c41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd749-6a2e-73e1-8725-292e71c177f8" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6a2e-7362-ab59-55eaa3238c41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6a2e-7362-ab59-55eaa3238c41_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6a2e-7362-ab59-55eaa3238c41" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6a2e-7362-ab59-55eaa3238c41_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6a2e-76e3-9f0f-7a294ce4a8f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6a2e-7362-ab59-55eaa3238c41" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6a2e-76e3-9f0f-7a294ce4a8f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6a2e-7cb7-a8c0-34826117bab2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6a2e-76e3-9f0f-7a294ce4a8f5" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6a2e-7cb7-a8c0-34826117bab2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6a2e-734e-97ce-304e462486fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6a2e-76e3-9f0f-7a294ce4a8f5" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6a2e-734e-97ce-304e462486fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6a2e-754b-be57-a2614e455205" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6a2e-76e3-9f0f-7a294ce4a8f5" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6a2e-754b-be57-a2614e455205" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_019fd749-6a2e-76aa-ae2d-693a1b4b6928" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6a2e-76e3-9f0f-7a294ce4a8f5" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_019fd749-6a2e-76aa-ae2d-693a1b4b6928" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd749-6a2e-7b10-b2e5-c626ac34b024" xlink:to="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndDueFromBanks_019fd749-6a2e-7523-bf8f-be52ab9810e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndDueFromBanks"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_CashAndDueFromBanks_019fd749-6a2e-7523-bf8f-be52ab9810e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestBearingDepositsInBanks_019fd749-6a2e-768b-baee-06e94694934a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestBearingDepositsInBanks"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_InterestBearingDepositsInBanks_019fd749-6a2e-768b-baee-06e94694934a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fd749-6a2e-72c5-b514-5a9d783cd078" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fd749-6a2e-72c5-b514-5a9d783cd078" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019fd749-6a2e-78cf-80a7-c60f46b87388" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019fd749-6a2e-78cf-80a7-c60f46b87388" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019fd749-6a2e-7100-ade7-cb3563cb9e68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019fd749-6a2e-7100-ade7-cb3563cb9e68" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6a2e-7333-b401-0396065d9cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6a2e-7333-b401-0396065d9cdb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_019fd749-6a2e-7612-9e61-b7b63f26d7bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_019fd749-6a2e-7612-9e61-b7b63f26d7bd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup_019fd749-6a2e-7589-8926-1f1a19aec02c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup_019fd749-6a2e-7589-8926-1f1a19aec02c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLossAbstract_019fd749-6a2e-7ad6-9b99-eb1602a2cd19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLossAbstract_019fd749-6a2e-7ad6-9b99-eb1602a2cd19" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6a2e-7a3c-a3f9-bae830fdfac4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLossAbstract_019fd749-6a2e-7ad6-9b99-eb1602a2cd19" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6a2e-7a3c-a3f9-bae830fdfac4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019fd749-6a2e-76d9-b6e0-b49d7d3b9968" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLossAbstract_019fd749-6a2e-7ad6-9b99-eb1602a2cd19" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019fd749-6a2e-76d9-b6e0-b49d7d3b9968" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6a2e-7c75-bdee-fc6ac7bce0c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLossAbstract_019fd749-6a2e-7ad6-9b99-eb1602a2cd19" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6a2e-7c75-bdee-fc6ac7bce0c8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_019fd749-6a2e-74f3-a619-df41afbe5100" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_019fd749-6a2e-74f3-a619-df41afbe5100" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fd749-6a2e-722c-848c-0c66ebc87480" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_Goodwill_019fd749-6a2e-722c-848c-0c66ebc87480" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fd749-6a2e-73b7-b58d-bdf956c22d00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fd749-6a2e-73b7-b58d-bdf956c22d00" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BankOwnedLifeInsurance_019fd749-6a2e-7f32-9414-f97e88db8a3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BankOwnedLifeInsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_BankOwnedLifeInsurance_019fd749-6a2e-7f32-9414-f97e88db8a3d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivableAndOtherAssets_019fd749-6a2e-7876-ae5b-cb7cfa384e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestReceivableAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_InterestReceivableAndOtherAssets_019fd749-6a2e-7876-ae5b-cb7cfa384e5d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019fd749-6a2e-79cc-b072-7afdbc4e9f7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019fd749-6a2e-7d5e-bc3e-7db4946893af" xlink:to="loc_us-gaap_Assets_019fd749-6a2e-79cc-b072-7afdbc4e9f7b" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd749-6a2e-7b10-b2e5-c626ac34b024" xlink:to="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsAbstract_019fd749-6a2e-7993-9eb0-92935e2a4b1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_DepositsAbstract_019fd749-6a2e-7993-9eb0-92935e2a4b1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestBearingDepositLiabilitiesDomestic_019fd749-6a2e-77c9-87cc-9dc28295ab1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestBearingDepositLiabilitiesDomestic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsAbstract_019fd749-6a2e-7993-9eb0-92935e2a4b1f" xlink:to="loc_us-gaap_NoninterestBearingDepositLiabilitiesDomestic_019fd749-6a2e-77c9-87cc-9dc28295ab1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsByTypeAbstract_019fd749-6a2e-7330-a045-b42887bd07d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsByTypeAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsAbstract_019fd749-6a2e-7993-9eb0-92935e2a4b1f" xlink:to="loc_us-gaap_DepositsByTypeAbstract_019fd749-6a2e-7330-a045-b42887bd07d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsNegotiableOrderOfWithdrawalNOW_019fd749-6a2e-7c50-99fb-9d207f0f56d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsNegotiableOrderOfWithdrawalNOW"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsByTypeAbstract_019fd749-6a2e-7330-a045-b42887bd07d0" xlink:to="loc_us-gaap_DepositsNegotiableOrderOfWithdrawalNOW_019fd749-6a2e-7c50-99fb-9d207f0f56d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsSavingsDeposits_019fd749-6a2e-71bd-a092-dc37fdd01ef6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsSavingsDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsByTypeAbstract_019fd749-6a2e-7330-a045-b42887bd07d0" xlink:to="loc_us-gaap_DepositsSavingsDeposits_019fd749-6a2e-71bd-a092-dc37fdd01ef6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsMoneyMarketDeposits_019fd749-6a2e-7da5-9325-6a2418b24de9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsMoneyMarketDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsByTypeAbstract_019fd749-6a2e-7330-a045-b42887bd07d0" xlink:to="loc_us-gaap_DepositsMoneyMarketDeposits_019fd749-6a2e-7da5-9325-6a2418b24de9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeDeposits_019fd749-6a2e-7800-a87f-d8b0899ad33f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimeDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsByTypeAbstract_019fd749-6a2e-7330-a045-b42887bd07d0" xlink:to="loc_us-gaap_TimeDeposits_019fd749-6a2e-7800-a87f-d8b0899ad33f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Deposits_019fd749-6a2e-71f3-910e-59212502ef0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Deposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsAbstract_019fd749-6a2e-7993-9eb0-92935e2a4b1f" xlink:to="loc_us-gaap_Deposits_019fd749-6a2e-71f3-910e-59212502ef0e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsPurchased_019fd749-6a2e-7d6d-a4a8-b4ebaa518353" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalFundsPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_FederalFundsPurchased_019fd749-6a2e-7d6d-a4a8-b4ebaa518353" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019fd749-6a2e-7432-a46c-b0f855a713ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019fd749-6a2e-7432-a46c-b0f855a713ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvancesFromFederalHomeLoanBanks_019fd749-6a2e-7995-923d-1ba58374233c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdvancesFromFederalHomeLoanBanks"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_AdvancesFromFederalHomeLoanBanks_019fd749-6a2e-7995-923d-1ba58374233c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherBorrowings_019fd749-6a2e-7b87-a2fc-3df39ab0389f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_OtherBorrowings_019fd749-6a2e-7b87-a2fc-3df39ab0389f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019fd749-6a2e-7292-9407-e09c30800c54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019fd749-6a2e-7292-9407-e09c30800c54" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019fd749-6a2e-7e1f-b5eb-46eb4786fb89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_Liabilities_019fd749-6a2e-7e1f-b5eb-46eb4786fb89" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019fd749-6a2e-790e-8e41-77a3236fd9b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019fd749-6a2e-790e-8e41-77a3236fd9b8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_019fd749-6a2e-7246-81ad-aa0e9fa1d04a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd749-6a2e-790e-8e41-77a3236fd9b8" xlink:to="loc_us-gaap_PreferredStockValue_019fd749-6a2e-7246-81ad-aa0e9fa1d04a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019fd749-6a2e-7a12-9690-acaeda031289" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd749-6a2e-790e-8e41-77a3236fd9b8" xlink:to="loc_us-gaap_CommonStockValue_019fd749-6a2e-7a12-9690-acaeda031289" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019fd749-6a2e-71a3-9e8b-6573944ee710" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd749-6a2e-790e-8e41-77a3236fd9b8" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019fd749-6a2e-71a3-9e8b-6573944ee710" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019fd749-6a2e-74db-9885-6bd73ea0e4db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd749-6a2e-790e-8e41-77a3236fd9b8" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019fd749-6a2e-74db-9885-6bd73ea0e4db" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019fd749-6a2e-7857-9ce4-94fd886b7d9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd749-6a2e-790e-8e41-77a3236fd9b8" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019fd749-6a2e-7857-9ce4-94fd886b7d9f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fd749-6a2e-7631-b931-8e688c092bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019fd749-6a2e-790e-8e41-77a3236fd9b8" xlink:to="loc_us-gaap_StockholdersEquity_019fd749-6a2e-7631-b931-8e688c092bf6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019fd749-6a2e-7eae-afe1-91d7ed4dc015" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019fd749-6a2e-7509-8a44-b57ecf2fa527" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019fd749-6a2e-7eae-afe1-91d7ed4dc015" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITYunaudited" xlink:type="simple" xlink:href="onb-20260930.xsd#CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITYunaudited"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITYunaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fd749-6a2e-7e1c-9244-ea3373588f38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019fd749-6a2e-7b99-867f-5fd70018b51a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019fd749-6a2e-7e1c-9244-ea3373588f38" xlink:to="loc_us-gaap_StatementTable_019fd749-6a2e-7b99-867f-5fd70018b51a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6a2e-76e5-9ed6-36b06018cca2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019fd749-6a2e-7b99-867f-5fd70018b51a" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6a2e-76e5-9ed6-36b06018cca2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-76e5-9ed6-36b06018cca2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6a2e-76e5-9ed6-36b06018cca2" xlink:to="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-76e5-9ed6-36b06018cca2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-7462-b3cc-3181abb981c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6a2e-76e5-9ed6-36b06018cca2" xlink:to="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-7462-b3cc-3181abb981c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_019fd749-6a2e-7d7f-b457-55781c075477" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-7462-b3cc-3181abb981c4" xlink:to="loc_us-gaap_PreferredStockMember_019fd749-6a2e-7d7f-b457-55781c075477" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fd749-6a2e-75a6-9ba5-989325b61720" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-7462-b3cc-3181abb981c4" xlink:to="loc_us-gaap_CommonStockMember_019fd749-6a2e-75a6-9ba5-989325b61720" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019fd749-6a2e-7ae7-8ecd-aac6489d7e8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-7462-b3cc-3181abb981c4" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019fd749-6a2e-7ae7-8ecd-aac6489d7e8b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019fd749-6a2e-7bac-a7df-44751c6191b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-7462-b3cc-3181abb981c4" xlink:to="loc_us-gaap_RetainedEarningsMember_019fd749-6a2e-7bac-a7df-44751c6191b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd749-6a2e-7541-9de2-fd8979f96da1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6a2e-7462-b3cc-3181abb981c4" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd749-6a2e-7541-9de2-fd8979f96da1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019fd749-6a2e-7e1c-9244-ea3373588f38" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fd749-6a2e-7ed1-8021-940711fbdd86" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_us-gaap_StockholdersEquity_019fd749-6a2e-7ed1-8021-940711fbdd86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fd749-6a2e-7cc2-a5ad-b37a7bc8f8be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_us-gaap_NetIncomeLoss_019fd749-6a2e-7cc2-a5ad-b37a7bc8f8be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019fd749-6a2e-7f9a-a560-489093803afc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019fd749-6a2e-7f9a-a560-489093803afc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019fd749-6a2e-782a-9598-74e1c88301bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019fd749-6a2e-782a-9598-74e1c88301bf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsAbstract_019fd749-6a2e-77fb-90ab-6b70abe05f16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_us-gaap_DividendsAbstract_019fd749-6a2e-77fb-90ab-6b70abe05f16" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_019fd749-6a2e-7591-92c4-43db14c1befd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsAbstract_019fd749-6a2e-77fb-90ab-6b70abe05f16" xlink:to="loc_us-gaap_DividendsCommonStock_019fd749-6a2e-7591-92c4-43db14c1befd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_019fd749-6a2e-7b8c-8676-290148cbadbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsAbstract_019fd749-6a2e-77fb-90ab-6b70abe05f16" xlink:to="loc_us-gaap_DividendsPreferredStock_019fd749-6a2e-7b8c-8676-290148cbadbc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019fd749-6a2e-7ff7-9745-5a01fce531cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019fd749-6a2e-7ff7-9745-5a01fce531cc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_StockIssuedDuringPeriodValueForwardSaleAgreements_019fd749-6a2e-7d0e-ac9a-eaa785786f3d" xlink:href="onb-20260930.xsd#onb_StockIssuedDuringPeriodValueForwardSaleAgreements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_onb_StockIssuedDuringPeriodValueForwardSaleAgreements_019fd749-6a2e-7d0e-ac9a-eaa785786f3d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_019fd749-6a2e-7773-83e3-565351322930" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_019fd749-6a2e-7773-83e3-565351322930" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fd749-6a2e-78e5-afbf-4524d309b0f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fd749-6a2e-78e5-afbf-4524d309b0f8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_SharesIssuedValueShareBasedPaymentArrangementIncludingStockDividends_019fd749-6a2e-7294-bf34-0b4e7a51d0b0" xlink:href="onb-20260930.xsd#onb_SharesIssuedValueShareBasedPaymentArrangementIncludingStockDividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fd749-6a2e-79d6-b665-ee775c2ee63f" xlink:to="loc_onb_SharesIssuedValueShareBasedPaymentArrangementIncludingStockDividends_019fd749-6a2e-7294-bf34-0b4e7a51d0b0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fd749-6a2e-7aa3-ad54-fcc04ed965ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/ACQUISITIONANDDIVESTITUREACTIVITYAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#ACQUISITIONANDDIVESTITUREACTIVITYAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/ACQUISITIONANDDIVESTITUREACTIVITYAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7630-8dbd-45a144bc9805" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7630-8dbd-45a144bc9805" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7bd3-9dac-9813f0cdc144" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7630-8dbd-45a144bc9805" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7bd3-9dac-9813f0cdc144" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7bd3-9dac-9813f0cdc144_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7bd3-9dac-9813f0cdc144" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7bd3-9dac-9813f0cdc144_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7348-9219-9a96311aceec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7bd3-9dac-9813f0cdc144" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7348-9219-9a96311aceec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BremerMember_019fd749-6ad3-7f2f-85bb-1e29d22c70f2" xlink:href="onb-20260930.xsd#onb_BremerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7348-9219-9a96311aceec" xlink:to="loc_onb_BremerMember_019fd749-6ad3-7f2f-85bb-1e29d22c70f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeAxis_019fd749-6ad3-778a-a1a8-2d59d3357ad7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForwardContractIndexedToIssuersEquityTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7630-8dbd-45a144bc9805" xlink:to="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeAxis_019fd749-6ad3-778a-a1a8-2d59d3357ad7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeDomain_019fd749-6ad3-778a-a1a8-2d59d3357ad7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForwardContractIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeAxis_019fd749-6ad3-778a-a1a8-2d59d3357ad7" xlink:to="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeDomain_019fd749-6ad3-778a-a1a8-2d59d3357ad7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeDomain_019fd749-6ad3-703e-9e51-d85c547b7e02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForwardContractIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeAxis_019fd749-6ad3-778a-a1a8-2d59d3357ad7" xlink:to="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeDomain_019fd749-6ad3-703e-9e51-d85c547b7e02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CitibankN.AMember_019fd749-6ad3-7d8e-8be3-f80c49600de6" xlink:href="onb-20260930.xsd#onb_CitibankN.AMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeDomain_019fd749-6ad3-703e-9e51-d85c547b7e02" xlink:to="loc_onb_CitibankN.AMember_019fd749-6ad3-7d8e-8be3-f80c49600de6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CitigroupGlobalMarketsInc.Member_019fd749-6ad3-74f5-b585-af0776304f76" xlink:href="onb-20260930.xsd#onb_CitigroupGlobalMarketsInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForwardContractIndexedToIssuersEquityTypeDomain_019fd749-6ad3-703e-9e51-d85c547b7e02" xlink:to="loc_onb_CitigroupGlobalMarketsInc.Member_019fd749-6ad3-74f5-b585-af0776304f76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6ad3-72fd-93a1-310dfc227b45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7630-8dbd-45a144bc9805" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6ad3-72fd-93a1-310dfc227b45" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6ad3-72fd-93a1-310dfc227b45_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6ad3-72fd-93a1-310dfc227b45" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6ad3-72fd-93a1-310dfc227b45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6ad3-71c1-8c18-aa30922b2a02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6ad3-72fd-93a1-310dfc227b45" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6ad3-71c1-8c18-aa30922b2a02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CoreDepositsMember_019fd749-6ad3-7a03-9b60-a487cce3907b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CoreDepositsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6ad3-71c1-8c18-aa30922b2a02" xlink:to="loc_us-gaap_CoreDepositsMember_019fd749-6ad3-7a03-9b60-a487cce3907b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019fd749-6ad3-7fda-a00a-c33f89c73b68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6ad3-71c1-8c18-aa30922b2a02" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019fd749-6ad3-7fda-a00a-c33f89c73b68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessAcquisitionEquityInterestIssuedOrIssuableCashPerShareAboveExchange_019fd749-6ad3-714b-9b26-79e4a9a09c9c" xlink:href="onb-20260930.xsd#onb_BusinessAcquisitionEquityInterestIssuedOrIssuableCashPerShareAboveExchange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_onb_BusinessAcquisitionEquityInterestIssuedOrIssuableCashPerShareAboveExchange_019fd749-6ad3-714b-9b26-79e4a9a09c9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessAcquisitionEquityInterestIssuedOrIssuableExchangeRatio_019fd749-6ad3-7a4b-9152-9db6b5e8c7d9" xlink:href="onb-20260930.xsd#onb_BusinessAcquisitionEquityInterestIssuedOrIssuableExchangeRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_onb_BusinessAcquisitionEquityInterestIssuedOrIssuableExchangeRatio_019fd749-6ad3-7a4b-9152-9db6b5e8c7d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractIndexedToIssuersEquityShares_019fd749-6ad3-7363-9b03-df3ca48e8483" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForwardContractIndexedToIssuersEquityShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_ForwardContractIndexedToIssuersEquityShares_019fd749-6ad3-7363-9b03-df3ca48e8483" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractIndexedToIssuersEquitySettlementAlternativesCashAtFairValue_019fd749-6ad3-7e00-9296-80e4e7d643c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForwardContractIndexedToIssuersEquitySettlementAlternativesCashAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_ForwardContractIndexedToIssuersEquitySettlementAlternativesCashAtFairValue_019fd749-6ad3-7e00-9296-80e4e7d643c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ForwardContractIndexedToIssuersEquityPeriodGrantedToPurchaseAdditionalShares_019fd749-6ad3-764f-881a-0c70c5769850" xlink:href="onb-20260930.xsd#onb_ForwardContractIndexedToIssuersEquityPeriodGrantedToPurchaseAdditionalShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_onb_ForwardContractIndexedToIssuersEquityPeriodGrantedToPurchaseAdditionalShares_019fd749-6ad3-764f-881a-0c70c5769850" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ForwardContractIndexedToIssuersEquityAdditionalNumberOfSharesToPurchase_019fd749-6ad3-7efe-af92-d6c8e3e89b2c" xlink:href="onb-20260930.xsd#onb_ForwardContractIndexedToIssuersEquityAdditionalNumberOfSharesToPurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_onb_ForwardContractIndexedToIssuersEquityAdditionalNumberOfSharesToPurchase_019fd749-6ad3-7efe-af92-d6c8e3e89b2c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ForwardContractIndexedToIssuersEquityAdditionalNumberOfShares_019fd749-6ad3-787f-a399-97ba44152356" xlink:href="onb-20260930.xsd#onb_ForwardContractIndexedToIssuersEquityAdditionalNumberOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_onb_ForwardContractIndexedToIssuersEquityAdditionalNumberOfShares_019fd749-6ad3-787f-a399-97ba44152356" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_019fd749-6ad3-7ff8-9523-6869b036fa1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_019fd749-6ad3-7ff8-9523-6869b036fa1e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019fd749-6ad3-72c7-86c3-6aad7ebdd78e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019fd749-6ad3-72c7-86c3-6aad7ebdd78e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019fd749-6ad3-758b-88e9-f22649b090d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019fd749-6ad3-758b-88e9-f22649b090d8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtPurchasePrice_019fd749-6ad3-7c64-a467-5ef05d97b3ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtPurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtPurchasePrice_019fd749-6ad3-7c64-a467-5ef05d97b3ee" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtParValue_019fd749-6ad3-795a-b8cf-fa95a8d46894" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtParValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtParValue_019fd749-6ad3-795a-b8cf-fa95a8d46894" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate_019fd749-6ad3-75a3-abdd-ba0689bdc8e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate_019fd749-6ad3-75a3-abdd-ba0689bdc8e9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationAcquisitionAndIntegrationRelatedCosts_019fd749-6ad3-7b67-976e-8b8eb8e15acc" xlink:href="onb-20260930.xsd#onb_BusinessCombinationAcquisitionAndIntegrationRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7d2d-87cb-0bbc1a7cc75e" xlink:to="loc_onb_BusinessCombinationAcquisitionAndIntegrationRelatedCosts_019fd749-6ad3-7b67-976e-8b8eb8e15acc" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/ACQUISITIONANDDIVESTITUREACTIVITYScheduleofAssetsAcquiredandLiabilitiesAssumedandtheFairValueofConsiderationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#ACQUISITIONANDDIVESTITUREACTIVITYScheduleofAssetsAcquiredandLiabilitiesAssumedandtheFairValueofConsiderationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/ACQUISITIONANDDIVESTITUREACTIVITYScheduleofAssetsAcquiredandLiabilitiesAssumedandtheFairValueofConsiderationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7844-a673-cebf6c9dfd8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7bb2-95e2-04706d3606d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7844-a673-cebf6c9dfd8a" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7bb2-95e2-04706d3606d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7566-84d8-bf5570e73891" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7bb2-95e2-04706d3606d2" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7566-84d8-bf5570e73891" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7566-84d8-bf5570e73891_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7566-84d8-bf5570e73891" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7566-84d8-bf5570e73891_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7d73-97e5-2f06a50b8a7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7566-84d8-bf5570e73891" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7d73-97e5-2f06a50b8a7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BremerMember_019fd749-6ad3-7214-a05c-ea7f75ecd038" xlink:href="onb-20260930.xsd#onb_BremerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7d73-97e5-2f06a50b8a7b" xlink:to="loc_onb_BremerMember_019fd749-6ad3-7214-a05c-ea7f75ecd038" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6ad3-7295-814c-415b11528c50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fd749-6ad3-7bb2-95e2-04706d3606d2" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6ad3-7295-814c-415b11528c50" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd749-6ad3-7295-814c-415b11528c50_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6ad3-7295-814c-415b11528c50" xlink:to="loc_us-gaap_EquityComponentDomain_019fd749-6ad3-7295-814c-415b11528c50_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd749-6ad3-7a8f-8d5b-0140442eb7f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6ad3-7295-814c-415b11528c50" xlink:to="loc_us-gaap_EquityComponentDomain_019fd749-6ad3-7a8f-8d5b-0140442eb7f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fd749-6ad3-7673-b4cd-993688880e31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6ad3-7a8f-8d5b-0140442eb7f3" xlink:to="loc_us-gaap_CommonStockMember_019fd749-6ad3-7673-b4cd-993688880e31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7844-a673-cebf6c9dfd8a" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019fd749-6ad3-7df9-9f8c-d96889dc6ac9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019fd749-6ad3-7df9-9f8c-d96889dc6ac9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedAssetAcquiredInvestmentInEquitySecurities_019fd749-6ad3-7404-944a-ba736cf83e2d" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedAssetAcquiredInvestmentInEquitySecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_onb_BusinessCombinationRecognizedAssetAcquiredInvestmentInEquitySecurities_019fd749-6ad3-7404-944a-ba736cf83e2d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities_019fd749-6ad3-7e4c-9d6d-f10bc3fba29f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities_019fd749-6ad3-7e4c-9d6d-f10bc3fba29f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFHLBFederalReserveBankStock_019fd749-6ad3-70d8-8a76-f63fc505e54f" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFHLBFederalReserveBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFHLBFederalReserveBankStock_019fd749-6ad3-70d8-8a76-f63fc505e54f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansHeldForSale_019fd749-6ad3-791f-bff9-a8ebde927f6a" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansHeldForSale_019fd749-6ad3-791f-bff9-a8ebde927f6a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoan_019fd749-6ad3-751a-bfa7-57f98b541b45" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoan_019fd749-6ad3-751a-bfa7-57f98b541b45" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019fd749-6ad3-7869-9118-030d312fa944" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019fd749-6ad3-7869-9118-030d312fa944" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fd749-6ad3-709b-bdd2-72c692dd461f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_us-gaap_Goodwill_019fd749-6ad3-709b-bdd2-72c692dd461f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019fd749-6ad3-76e7-b642-f0968039707d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_019fd749-6ad3-76e7-b642-f0968039707d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCompanyOwnedLifeInsurance_019fd749-6ad3-7366-ac0f-05666a605cf2" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCompanyOwnedLifeInsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCompanyOwnedLifeInsurance_019fd749-6ad3-7366-ac0f-05666a605cf2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019fd749-6ad3-7aae-a1c6-691942e0feb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019fd749-6ad3-7aae-a1c6-691942e0feb2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_019fd749-6ad3-74ee-a074-7b08298d126f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_019fd749-6ad3-7846-bae1-1d7735d9c948" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_019fd749-6ad3-74ee-a074-7b08298d126f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019fd749-6ad3-7237-8874-19d1b30bac17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7844-a673-cebf6c9dfd8a" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019fd749-6ad3-7237-8874-19d1b30bac17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesDeposits_019fd749-6ad3-700a-a4c0-0425b30cbf57" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019fd749-6ad3-7237-8874-19d1b30bac17" xlink:to="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesDeposits_019fd749-6ad3-700a-a4c0-0425b30cbf57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019fd749-6ad3-7f25-9e5b-92baf9a8c259" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019fd749-6ad3-7237-8874-19d1b30bac17" xlink:to="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019fd749-6ad3-7f25-9e5b-92baf9a8c259" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesFederalHomeLoanBankAdvances_019fd749-6ad3-76f9-81c8-1a95b6f12181" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesFederalHomeLoanBankAdvances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019fd749-6ad3-7237-8874-19d1b30bac17" xlink:to="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesFederalHomeLoanBankAdvances_019fd749-6ad3-76f9-81c8-1a95b6f12181" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOtherBorrowings_019fd749-6ad3-7924-b3ce-c1b84dbc56f4" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOtherBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019fd749-6ad3-7237-8874-19d1b30bac17" xlink:to="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOtherBorrowings_019fd749-6ad3-7924-b3ce-c1b84dbc56f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesAccruedExpensesAndOtherLiabilities_019fd749-6ad3-7873-965e-c12ed26ebc80" xlink:href="onb-20260930.xsd#onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesAccruedExpensesAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019fd749-6ad3-7237-8874-19d1b30bac17" xlink:to="loc_onb_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesAccruedExpensesAndOtherLiabilities_019fd749-6ad3-7873-965e-c12ed26ebc80" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_019fd749-6ad3-7795-894b-758bd805d7b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract_019fd749-6ad3-7237-8874-19d1b30bac17" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_019fd749-6ad3-7795-894b-758bd805d7b2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd749-6ad3-7167-bded-69e4b50dc5ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferredAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7844-a673-cebf6c9dfd8a" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd749-6ad3-7167-bded-69e4b50dc5ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019fd749-6ad3-78e9-99a3-10196cc94b8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd749-6ad3-7167-bded-69e4b50dc5ab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019fd749-6ad3-78e9-99a3-10196cc94b8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fd749-6ad3-7ade-b8f7-0238aeb16a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd749-6ad3-7167-bded-69e4b50dc5ab" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fd749-6ad3-7ade-b8f7-0238aeb16a8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fd749-6ad3-7227-b9db-db5254f72383" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_019fd749-6ad3-7167-bded-69e4b50dc5ab" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fd749-6ad3-7227-b9db-db5254f72383" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fd749-6ad3-7fb3-9954-d38625ce472d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7844-a673-cebf6c9dfd8a" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fd749-6ad3-7fb3-9954-d38625ce472d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_019fd749-6ad3-701e-af7b-df76e949819a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fd749-6ad3-7844-a673-cebf6c9dfd8a" xlink:to="loc_us-gaap_SharePrice_019fd749-6ad3-701e-af7b-df76e949819a" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/INVESTMENTSECURITIESScheduleofAmortizedCostandFairValueofAvailableforSaleInvestmentSecuritiesPortfolioDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#INVESTMENTSECURITIESScheduleofAmortizedCostandFairValueofAvailableforSaleInvestmentSecuritiesPortfolioDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/INVESTMENTSECURITIESScheduleofAmortizedCostandFairValueofAvailableforSaleInvestmentSecuritiesPortfolioDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fd749-6ad3-7165-bfb7-822d4c7c51d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fd749-6ad3-779e-bbd5-9b4df21d2b4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fd749-6ad3-7165-bfb7-822d4c7c51d5" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fd749-6ad3-779e-bbd5-9b4df21d2b4a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-74d2-aa0d-84dab13918b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fd749-6ad3-779e-bbd5-9b4df21d2b4a" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-74d2-aa0d-84dab13918b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-74d2-aa0d-84dab13918b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-74d2-aa0d-84dab13918b4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-74d2-aa0d-84dab13918b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7ca6-a7fc-d1d5513204c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-74d2-aa0d-84dab13918b4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7ca6-a7fc-d1d5513204c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019fd749-6ad3-7d01-8da3-5024ddf45012" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7ca6-a7fc-d1d5513204c6" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019fd749-6ad3-7d01-8da3-5024ddf45012" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6ad3-7da7-962c-d5207c792e01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7ca6-a7fc-d1d5513204c6" xlink:to="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6ad3-7da7-962c-d5207c792e01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6ad3-7f01-bec6-3ebe8833b4da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7ca6-a7fc-d1d5513204c6" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6ad3-7f01-bec6-3ebe8833b4da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6ad3-7ff6-8414-c376867891bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7ca6-a7fc-d1d5513204c6" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6ad3-7ff6-8414-c376867891bf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_PooledTrustPreferredSecuritiesMember_019fd749-6ad3-702e-97e9-eedb65a85288" xlink:href="onb-20260930.xsd#onb_PooledTrustPreferredSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7ca6-a7fc-d1d5513204c6" xlink:to="loc_onb_PooledTrustPreferredSecuritiesMember_019fd749-6ad3-702e-97e9-eedb65a85288" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDebtSecuritiesMember_019fd749-6ad3-7234-b3e6-1930fd31ab5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7ca6-a7fc-d1d5513204c6" xlink:to="loc_us-gaap_OtherDebtSecuritiesMember_019fd749-6ad3-7234-b3e6-1930fd31ab5a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableforsaleAmortizedCostAbstract_019fd749-6ad3-7cfa-9de8-057d426fc940" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableforsaleAmortizedCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fd749-6ad3-7165-bfb7-822d4c7c51d5" xlink:to="loc_us-gaap_DebtSecuritiesAvailableforsaleAmortizedCostAbstract_019fd749-6ad3-7cfa-9de8-057d426fc940" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7146-9369-fb1caa311902" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAmortizedCostAbstract_019fd749-6ad3-7cfa-9de8-057d426fc940" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7146-9369-fb1caa311902" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019fd749-6ad3-78ed-af23-fcdb48a6f843" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAmortizedCostAbstract_019fd749-6ad3-7cfa-9de8-057d426fc940" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019fd749-6ad3-78ed-af23-fcdb48a6f843" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fd749-6ad3-700e-9b38-e99783393e3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAmortizedCostAbstract_019fd749-6ad3-7cfa-9de8-057d426fc940" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fd749-6ad3-700e-9b38-e99783393e3d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DebtSecuritiesAvailableForSaleAccumulatedBasisAdjustmentsBeforeTax_019fd749-6ad3-7078-bc5a-6245cc06b1b4" xlink:href="onb-20260930.xsd#onb_DebtSecuritiesAvailableForSaleAccumulatedBasisAdjustmentsBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAmortizedCostAbstract_019fd749-6ad3-7cfa-9de8-057d426fc940" xlink:to="loc_onb_DebtSecuritiesAvailableForSaleAccumulatedBasisAdjustmentsBeforeTax_019fd749-6ad3-7078-bc5a-6245cc06b1b4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019fd749-6ad3-71a8-9d01-210baf9ef56a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAmortizedCostAbstract_019fd749-6ad3-7cfa-9de8-057d426fc940" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019fd749-6ad3-71a8-9d01-210baf9ef56a" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/INVESTMENTSECURITIESScheduleofAmortizedCostandFairValueHeldtoMaturityDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#INVESTMENTSECURITIESScheduleofAmortizedCostandFairValueHeldtoMaturityDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/INVESTMENTSECURITIESScheduleofAmortizedCostandFairValueHeldtoMaturityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_019fd749-6ad3-7899-b426-9fe8858a08c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_019fd749-6ad3-7b7d-b796-25d8cc131ea3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_019fd749-6ad3-7899-b426-9fe8858a08c5" xlink:to="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_019fd749-6ad3-7b7d-b796-25d8cc131ea3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-76b0-aa8b-7b5e3ae5d598" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_019fd749-6ad3-7b7d-b796-25d8cc131ea3" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-76b0-aa8b-7b5e3ae5d598" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-76b0-aa8b-7b5e3ae5d598_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-76b0-aa8b-7b5e3ae5d598" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-76b0-aa8b-7b5e3ae5d598_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7261-b6cf-88ebe4228f3e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-76b0-aa8b-7b5e3ae5d598" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7261-b6cf-88ebe4228f3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6ad3-76e6-9374-1f992a0e8136" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7261-b6cf-88ebe4228f3e" xlink:to="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6ad3-76e6-9374-1f992a0e8136" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6ad3-7402-8382-fc9f290bf8ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7261-b6cf-88ebe4228f3e" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6ad3-7402-8382-fc9f290bf8ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6ad3-7f73-81c6-454645994ec2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-7261-b6cf-88ebe4228f3e" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6ad3-7f73-81c6-454645994ec2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract_019fd749-6ad3-7cc4-8ca7-a935aca254fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_019fd749-6ad3-7899-b426-9fe8858a08c5" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract_019fd749-6ad3-7cc4-8ca7-a935aca254fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7036-b95e-51aa7147a7e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract_019fd749-6ad3-7cc4-8ca7-a935aca254fb" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7036-b95e-51aa7147a7e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-73e1-b466-b1397ac7b8b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract_019fd749-6ad3-7cc4-8ca7-a935aca254fb" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-73e1-b466-b1397ac7b8b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6ad3-77ed-8c56-8a5c78223334" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract_019fd749-6ad3-7cc4-8ca7-a935aca254fb" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6ad3-77ed-8c56-8a5c78223334" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_019fd749-6ad3-7343-b9dd-f37b6d89382a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract_019fd749-6ad3-7cc4-8ca7-a935aca254fb" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_019fd749-6ad3-7343-b9dd-f37b6d89382a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_019fd749-6ad3-7605-8366-e67d7901e6e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract_019fd749-6ad3-7cc4-8ca7-a935aca254fb" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_019fd749-6ad3-7605-8366-e67d7901e6e5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesFairValue_019fd749-6ad3-74ba-93ff-ded001d79923" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNetCarryingAmountAbstract_019fd749-6ad3-7cc4-8ca7-a935aca254fb" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesFairValue_019fd749-6ad3-74ba-93ff-ded001d79923" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/INVESTMENTSECURITIESScheduleofAvailableforSaleandHeldtoMaturityInvestmentSecuritieswithUnrealizedLossesbyAggregatedMajorSecurityTypeandLengthofTimeinContinuousUnrealizedLossPositionDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#INVESTMENTSECURITIESScheduleofAvailableforSaleandHeldtoMaturityInvestmentSecuritieswithUnrealizedLossesbyAggregatedMajorSecurityTypeandLengthofTimeinContinuousUnrealizedLossPositionDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/INVESTMENTSECURITIESScheduleofAvailableforSaleandHeldtoMaturityInvestmentSecuritieswithUnrealizedLossesbyAggregatedMajorSecurityTypeandLengthofTimeinContinuousUnrealizedLossPositionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7c7c-b1f2-d1eee653fb8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTable_019fd749-6ad3-7543-afc8-60651a15954e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7c7c-b1f2-d1eee653fb8d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTable_019fd749-6ad3-7543-afc8-60651a15954e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-73f0-bfb8-8f6fc58c01c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTable_019fd749-6ad3-7543-afc8-60651a15954e" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-73f0-bfb8-8f6fc58c01c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-73f0-bfb8-8f6fc58c01c6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-73f0-bfb8-8f6fc58c01c6" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-73f0-bfb8-8f6fc58c01c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71b6-8cb0-a2f9e80046a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-73f0-bfb8-8f6fc58c01c6" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71b6-8cb0-a2f9e80046a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019fd749-6ad3-7f14-976c-9c6d81f783ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71b6-8cb0-a2f9e80046a2" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019fd749-6ad3-7f14-976c-9c6d81f783ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6ad3-713f-9ac1-bd74eb9958e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71b6-8cb0-a2f9e80046a2" xlink:to="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6ad3-713f-9ac1-bd74eb9958e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6ad3-704e-a46c-382884bbbd41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71b6-8cb0-a2f9e80046a2" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6ad3-704e-a46c-382884bbbd41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6ad3-792b-899d-f1d7aac4166e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71b6-8cb0-a2f9e80046a2" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6ad3-792b-899d-f1d7aac4166e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_PooledTrustPreferredSecuritiesMember_019fd749-6ad3-792d-a43c-0794c4359274" xlink:href="onb-20260930.xsd#onb_PooledTrustPreferredSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71b6-8cb0-a2f9e80046a2" xlink:to="loc_onb_PooledTrustPreferredSecuritiesMember_019fd749-6ad3-792d-a43c-0794c4359274" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDebtSecuritiesMember_019fd749-6ad3-7d75-8312-4e35830cceae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71b6-8cb0-a2f9e80046a2" xlink:to="loc_us-gaap_OtherDebtSecuritiesMember_019fd749-6ad3-7d75-8312-4e35830cceae" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019fd749-6ad3-7c27-af3a-d956ded7153d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7c7c-b1f2-d1eee653fb8d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019fd749-6ad3-7c27-af3a-d956ded7153d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019fd749-6ad3-7cad-ad8b-0c87189bdd03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7c7c-b1f2-d1eee653fb8d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019fd749-6ad3-7cad-ad8b-0c87189bdd03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019fd749-6ad3-7207-a0f3-d526399a071a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7c7c-b1f2-d1eee653fb8d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019fd749-6ad3-7207-a0f3-d526399a071a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fd749-6ad3-70b2-a9c3-8ed33238fe1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7c7c-b1f2-d1eee653fb8d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fd749-6ad3-70b2-a9c3-8ed33238fe1a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019fd749-6ad3-72ca-a60a-4446a014c7ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7c7c-b1f2-d1eee653fb8d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019fd749-6ad3-72ca-a60a-4446a014c7ed" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fd749-6ad3-717a-ba2a-a9d4894e6920" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7c7c-b1f2-d1eee653fb8d" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fd749-6ad3-717a-ba2a-a9d4894e6920" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/INVESTMENTSECURITIESScheduleofHeldtoMaturitywithUnrecognizedLossesDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#INVESTMENTSECURITIESScheduleofHeldtoMaturitywithUnrecognizedLossesDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/INVESTMENTSECURITIESScheduleofHeldtoMaturitywithUnrecognizedLossesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_019fd749-6ad3-711b-82b5-ea534fcbd452" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_019fd749-6ad3-7765-8d8e-143190088ade" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_019fd749-6ad3-711b-82b5-ea534fcbd452" xlink:to="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_019fd749-6ad3-7765-8d8e-143190088ade" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-71bb-ac5d-29f106fb1b18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_019fd749-6ad3-7765-8d8e-143190088ade" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-71bb-ac5d-29f106fb1b18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71bb-ac5d-29f106fb1b18_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-71bb-ac5d-29f106fb1b18" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-71bb-ac5d-29f106fb1b18_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-79fd-babf-25ff507fc8e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6ad3-71bb-ac5d-29f106fb1b18" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-79fd-babf-25ff507fc8e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6ad3-7be8-893a-8a12e062487a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-79fd-babf-25ff507fc8e8" xlink:to="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6ad3-7be8-893a-8a12e062487a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6ad3-76f3-9676-4e726ddfdcb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-79fd-babf-25ff507fc8e8" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6ad3-76f3-9676-4e726ddfdcb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6ad3-7a3b-a840-e3424595205e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6ad3-79fd-babf-25ff507fc8e8" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6ad3-7a3b-a840-e3424595205e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7093-914e-e4c5841a1664" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_019fd749-6ad3-711b-82b5-ea534fcbd452" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7093-914e-e4c5841a1664" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_019fd749-6ad3-7fb2-84a9-127fd3035c9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7093-914e-e4c5841a1664" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_019fd749-6ad3-7fb2-84a9-127fd3035c9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_019fd749-6ad3-7102-bdb0-8a1e57bada75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7093-914e-e4c5841a1664" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_019fd749-6ad3-7102-bdb0-8a1e57bada75" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue_019fd749-6ad3-7ad7-8133-dd74c6757d59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValueAbstract_019fd749-6ad3-7093-914e-e4c5841a1664" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue_019fd749-6ad3-7ad7-8133-dd74c6757d59" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fd749-6ad3-7e8b-8741-18327ff280e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_019fd749-6ad3-711b-82b5-ea534fcbd452" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fd749-6ad3-7e8b-8741-18327ff280e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019fd749-6ad3-795d-a5dc-de83c9acaab6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fd749-6ad3-7e8b-8741-18327ff280e0" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019fd749-6ad3-795d-a5dc-de83c9acaab6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fd749-6ad3-7199-bb16-faddc42e05b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fd749-6ad3-7e8b-8741-18327ff280e0" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fd749-6ad3-7199-bb16-faddc42e05b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss_019fd749-6ad3-7a88-9e78-7e247831ab12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fd749-6ad3-7e8b-8741-18327ff280e0" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss_019fd749-6ad3-7a88-9e78-7e247831ab12" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/INVESTMENTSECURITIESAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#INVESTMENTSECURITIESAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/INVESTMENTSECURITIESAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SummaryOfInvestmentHoldingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SummaryOfInvestmentHoldingsTable_019fd749-6ad3-7327-b1b5-f15c1900ef8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SummaryOfInvestmentHoldingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_SummaryOfInvestmentHoldingsTable_019fd749-6ad3-7327-b1b5-f15c1900ef8d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019fd749-6ad3-7b62-b400-4f4de5aad9f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsTable_019fd749-6ad3-7327-b1b5-f15c1900ef8d" xlink:to="loc_us-gaap_InvestmentTypeAxis_019fd749-6ad3-7b62-b400-4f4de5aad9f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6ad3-7b62-b400-4f4de5aad9f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019fd749-6ad3-7b62-b400-4f4de5aad9f1" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6ad3-7b62-b400-4f4de5aad9f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6ad3-756f-be1e-88d1e26c11c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019fd749-6ad3-7b62-b400-4f4de5aad9f1" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6ad3-756f-be1e-88d1e26c11c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PartnershipInterestMember_019fd749-6ad3-7be9-bca1-18560d695419" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6ad3-756f-be1e-88d1e26c11c7" xlink:to="loc_srt_PartnershipInterestMember_019fd749-6ad3-7be9-bca1-18560d695419" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_InitiativesInLowToModerateIncomeNeighborhoodsMember_019fd749-6ad3-7d24-aa45-eb6a7e8fec05" xlink:href="onb-20260930.xsd#onb_InitiativesInLowToModerateIncomeNeighborhoodsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6ad3-756f-be1e-88d1e26c11c7" xlink:to="loc_onb_InitiativesInLowToModerateIncomeNeighborhoodsMember_019fd749-6ad3-7d24-aa45-eb6a7e8fec05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_TransfersFromAvailableForSaleToHeldToMaturity_019fd749-6ad3-747d-8b2d-2a4ede8e039a" xlink:href="onb-20260930.xsd#onb_TransfersFromAvailableForSaleToHeldToMaturity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_onb_TransfersFromAvailableForSaleToHeldToMaturity_019fd749-6ad3-747d-8b2d-2a4ede8e039a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-71f2-9e28-a3839067c23d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-71f2-9e28-a3839067c23d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList_019fd749-6ad3-78dc-89ba-dbe1d200f2c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList_019fd749-6ad3-78dc-89ba-dbe1d200f2c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-7a8f-b199-5af28573cddd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-7a8f-b199-5af28573cddd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss_019fd749-6ad3-74cd-bf11-e6d888fd76eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss_019fd749-6ad3-74cd-bf11-e6d888fd76eb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_NumberOfSecuritiesInSecurityPortfolio_019fd749-6ad3-75f1-ba22-41265818c5c0" xlink:href="onb-20260930.xsd#onb_NumberOfSecuritiesInSecurityPortfolio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_onb_NumberOfSecuritiesInSecurityPortfolio_019fd749-6ad3-75f1-ba22-41265818c5c0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019fd749-6ad3-7b81-b1a6-ff67fb0e3da8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019fd749-6ad3-7b81-b1a6-ff67fb0e3da8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019fd749-6ad3-7be3-8cc4-895be46ef9b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019fd749-6ad3-7be3-8cc4-895be46ef9b7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_019fd749-6ad3-7d36-8fdc-d0ac7318dfce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_019fd749-6ad3-7d36-8fdc-d0ac7318dfce" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_019fd749-6ad3-7eb5-994f-64a04f7d0b5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_019fd749-6ad3-7eb5-994f-64a04f7d0b5a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueImpairmentLossAnnualAmount_019fd749-6ad3-7be9-837a-9b1f7a91731c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueImpairmentLossAnnualAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6ad3-73b1-8ac9-efc5620cda4e" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueImpairmentLossAnnualAmount_019fd749-6ad3-7be9-837a-9b1f7a91731c" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7b84-bba5-5659f5f4bd26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7b84-bba5-5659f5f4bd26" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-77a5-ba66-c53fb3b58727" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7b84-bba5-5659f5f4bd26" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-77a5-ba66-c53fb3b58727" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-77a5-ba66-c53fb3b58727_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-77a5-ba66-c53fb3b58727" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-77a5-ba66-c53fb3b58727_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-70aa-bd63-b1b44d890633" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-77a5-ba66-c53fb3b58727" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-70aa-bd63-b1b44d890633" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-788d-831c-fc68e3c9e6e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-70aa-bd63-b1b44d890633" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-788d-831c-fc68e3c9e6e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7829-a3d5-fbb47e9f4f49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7b84-bba5-5659f5f4bd26" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7829-a3d5-fbb47e9f4f49" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7829-a3d5-fbb47e9f4f49_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7829-a3d5-fbb47e9f4f49" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7829-a3d5-fbb47e9f4f49_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-718e-ba1b-e400ae574274" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7829-a3d5-fbb47e9f4f49" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-718e-ba1b-e400ae574274" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BremerMember_019fd749-6ad3-722c-a691-48f612a86b69" xlink:href="onb-20260930.xsd#onb_BremerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-718e-ba1b-e400ae574274" xlink:to="loc_onb_BremerMember_019fd749-6ad3-722c-a691-48f612a86b69" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LoanParticipations_019fd749-6ad3-7b92-9e43-ab577b569a22" xlink:href="onb-20260930.xsd#onb_LoanParticipations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_onb_LoanParticipations_019fd749-6ad3-7b92-9e43-ab577b569a22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LoanParticipationsSold_019fd749-6ad3-7103-9502-f78deb8ed8af" xlink:href="onb-20260930.xsd#onb_LoanParticipationsSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_onb_LoanParticipationsSold_019fd749-6ad3-7103-9502-f78deb8ed8af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LoanParticipationsRetained_019fd749-6ad3-7d3d-9d49-04ae918effaa" xlink:href="onb-20260930.xsd#onb_LoanParticipationsRetained"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_onb_LoanParticipationsRetained_019fd749-6ad3-7d3d-9d49-04ae918effaa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FinancingReceivableNumberOfLoanPortfolios_019fd749-6ad3-74ca-9ea9-74719e894b65" xlink:href="onb-20260930.xsd#onb_FinancingReceivableNumberOfLoanPortfolios"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_onb_FinancingReceivableNumberOfLoanPortfolios_019fd749-6ad3-74ca-9ea9-74719e894b65" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FinancingReceivableNumberOfLoanSegments_019fd749-6ad3-78ad-af8a-a3642c8ea7a4" xlink:href="onb-20260930.xsd#onb_FinancingReceivableNumberOfLoanSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_onb_FinancingReceivableNumberOfLoanSegments_019fd749-6ad3-78ad-af8a-a3642c8ea7a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CommercialRealEstateLoansAsPercentageOfRiskBasedCapital_019fd749-6ad3-735b-b442-5ccd4e39e25d" xlink:href="onb-20260930.xsd#onb_CommercialRealEstateLoansAsPercentageOfRiskBasedCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_onb_CommercialRealEstateLoansAsPercentageOfRiskBasedCapital_019fd749-6ad3-735b-b442-5ccd4e39e25d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CommercialRealEstateLoansAsPercentageOfRiskBasedCapitalRegulatoryGuideLineLimit_019fd749-6ad3-723c-b534-1ee5a6ae0a64" xlink:href="onb-20260930.xsd#onb_CommercialRealEstateLoansAsPercentageOfRiskBasedCapitalRegulatoryGuideLineLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_onb_CommercialRealEstateLoansAsPercentageOfRiskBasedCapitalRegulatoryGuideLineLimit_019fd749-6ad3-723c-b534-1ee5a6ae0a64" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal_019fd749-6ad3-76f0-a6f8-a993f500e890" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal_019fd749-6ad3-76f0-a6f8-a993f500e890" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-75e3-9df0-065f00141f0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_us-gaap_FinancingReceivableAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-75e3-9df0-065f00141f0a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FinanceReceivablePastDuePeriodForNonaccrualStatus_019fd749-6ad3-78ea-8587-3deaeeb537d3" xlink:href="onb-20260930.xsd#onb_FinanceReceivablePastDuePeriodForNonaccrualStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_onb_FinanceReceivablePastDuePeriodForNonaccrualStatus_019fd749-6ad3-78ea-8587-3deaeeb537d3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1_019fd749-6ad3-744d-a501-e227a61649bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1_019fd749-6ad3-744d-a501-e227a61649bd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend_019fd749-6ad3-784e-aa04-a5bf764bc22d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7025-90e0-0786527aacae" xlink:to="loc_us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend_019fd749-6ad3-784e-aa04-a5bf764bc22d" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofCompositionofLoansandImpactofAdoptionDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofCompositionofLoansandImpactofAdoptionDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofCompositionofLoansandImpactofAdoptionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7bf7-b744-246b32e223fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7538-89c1-69da02c25b72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7bf7-b744-246b32e223fe" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7538-89c1-69da02c25b72" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7a36-b2ba-9144ee341907" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7538-89c1-69da02c25b72" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7a36-b2ba-9144ee341907" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7a36-b2ba-9144ee341907_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7a36-b2ba-9144ee341907" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7a36-b2ba-9144ee341907_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7a36-b2ba-9144ee341907" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-762d-bd49-ebd69e0db5bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-762d-bd49-ebd69e0db5bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7c01-9c3f-9b7deacaa119" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7c01-9c3f-9b7deacaa119" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7c6f-92e1-8a49b287da62" xlink:href="onb-20260930.xsd#onb_BusinessBankingCreditCenterPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7c6f-92e1-8a49b287da62" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-7894-8b42-9921d158faa0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-7894-8b42-9921d158faa0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_019fd749-6ad3-7bef-9c5c-9d352417eef2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_019fd749-6ad3-7bef-9c5c-9d352417eef2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7f4b-9be1-a8244b2d7612" xlink:href="onb-20260930.xsd#onb_IndirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7f4b-9be1-a8244b2d7612" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-73f7-aa6f-31c8eeff3b45" xlink:href="onb-20260930.xsd#onb_DirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-73f7-aa6f-31c8eeff3b45" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-79ad-8457-157221348bf2" xlink:href="onb-20260930.xsd#onb_HomeEquityPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-79ad-8457-157221348bf2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherConsumerSegmentMember_01a157fa-5e7a-7437-a36f-f33bc306e264" xlink:href="onb-20260930.xsd#onb_OtherConsumerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_onb_OtherConsumerSegmentMember_01a157fa-5e7a-7437-a36f-f33bc306e264" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeasesPortfolioSegmentMember_019fd749-6ad3-7ec1-8fa9-eec2a2535401" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinanceLeasesPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7741-ba8a-085bd18b678c" xlink:to="loc_us-gaap_FinanceLeasesPortfolioSegmentMember_019fd749-6ad3-7ec1-8fa9-eec2a2535401" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-7d69-aece-cea35688d5f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7538-89c1-69da02c25b72" xlink:to="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-7d69-aece-cea35688d5f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7d69-aece-cea35688d5f5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-7d69-aece-cea35688d5f5" xlink:to="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7d69-aece-cea35688d5f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7bd9-93e9-c9e7d8fd7b76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-7d69-aece-cea35688d5f5" xlink:to="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7bd9-93e9-c9e7d8fd7b76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_SegmentPortfolioReclassificationMember_019fd749-6ad3-73fb-8fcb-dfc8220d9092" xlink:href="onb-20260930.xsd#onb_SegmentPortfolioReclassificationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7bd9-93e9-c9e7d8fd7b76" xlink:to="loc_onb_SegmentPortfolioReclassificationMember_019fd749-6ad3-73fb-8fcb-dfc8220d9092" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_SegmentPortfolioReclassificationAdjustedBalanceMember_019fd749-6ad3-7e3b-822e-9b1f611ecdb1" xlink:href="onb-20260930.xsd#onb_SegmentPortfolioReclassificationAdjustedBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7bd9-93e9-c9e7d8fd7b76" xlink:to="loc_onb_SegmentPortfolioReclassificationAdjustedBalanceMember_019fd749-6ad3-7e3b-822e-9b1f611ecdb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7ee7-8c63-e8c768dd2613" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7bf7-b744-246b32e223fe" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7ee7-8c63-e8c768dd2613" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-7ef1-84e3-29928b748163" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7bf7-b744-246b32e223fe" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-7ef1-84e3-29928b748163" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6ad3-75bb-ae76-9ba8e8ac5bb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7bf7-b744-246b32e223fe" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6ad3-75bb-ae76-9ba8e8ac5bb3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndFeeIncomeLoansAndLeases_019fd749-6ad3-7200-ac23-1af9775d166c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndFeeIncomeLoansAndLeases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7bf7-b744-246b32e223fe" xlink:to="loc_us-gaap_InterestAndFeeIncomeLoansAndLeases_019fd749-6ad3-7200-ac23-1af9775d166c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofActivityinAllowanceforLoanLossesDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofActivityinAllowanceforLoanLossesDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofActivityinAllowanceforLoanLossesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7812-a145-75f1dd41adc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-78b9-b07c-8896da1c35a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7812-a145-75f1dd41adc3" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-78b9-b07c-8896da1c35a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-715c-93d2-11708b1915f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-78b9-b07c-8896da1c35a4" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-715c-93d2-11708b1915f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-715c-93d2-11708b1915f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-715c-93d2-11708b1915f2" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-715c-93d2-11708b1915f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-715c-93d2-11708b1915f2" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-720e-9904-8061a5961c81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-720e-9904-8061a5961c81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7fc3-ba4f-f04e396f3426" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7fc3-ba4f-f04e396f3426" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7c98-bd77-eb890d024e68" xlink:href="onb-20260930.xsd#onb_BusinessBankingCreditCenterPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:to="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7c98-bd77-eb890d024e68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-7559-8b59-d7df4ffd41ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-7559-8b59-d7df4ffd41ce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7aba-822e-cc22d0db3b13" xlink:href="onb-20260930.xsd#onb_IndirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:to="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7aba-822e-cc22d0db3b13" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-7e2b-bdb9-48e40dc2e2cb" xlink:href="onb-20260930.xsd#onb_DirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:to="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-7e2b-bdb9-48e40dc2e2cb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-7829-aca8-f3cb3f4d5544" xlink:href="onb-20260930.xsd#onb_HomeEquityPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:to="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-7829-aca8-f3cb3f4d5544" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherConsumerSegmentMember_01a157f9-b748-759b-aba7-136da61fffef" xlink:href="onb-20260930.xsd#onb_OtherConsumerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7c8a-9745-e277d19575e4" xlink:to="loc_onb_OtherConsumerSegmentMember_01a157f9-b748-759b-aba7-136da61fffef" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019fd749-6ad3-74e3-bcac-1e072dbe2940" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7812-a145-75f1dd41adc3" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019fd749-6ad3-74e3-bcac-1e072dbe2940" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-79bf-a565-10785c151741" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019fd749-6ad3-74e3-bcac-1e072dbe2940" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-79bf-a565-10785c151741" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FinancingReceivableAllowanceForCreditLossRealignmentOfLoanPortfolioSegments_019fd749-6ad3-7650-94ef-8b7a3d9ad440" xlink:href="onb-20260930.xsd#onb_FinancingReceivableAllowanceForCreditLossRealignmentOfLoanPortfolioSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019fd749-6ad3-74e3-bcac-1e072dbe2940" xlink:to="loc_onb_FinancingReceivableAllowanceForCreditLossRealignmentOfLoanPortfolioSegments_019fd749-6ad3-7650-94ef-8b7a3d9ad440" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestPurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate_01a16998-d415-79ec-bfc4-1c9ca1857cdd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestPurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019fd749-6ad3-74e3-bcac-1e072dbe2940" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestPurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate_01a16998-d415-79ec-bfc4-1c9ca1857cdd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019fd749-6ad3-7ecf-9ef7-ad1d4a1878ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019fd749-6ad3-74e3-bcac-1e072dbe2940" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019fd749-6ad3-7ecf-9ef7-ad1d4a1878ef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery_019fd749-6ad3-703e-9d27-f8294b88a885" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019fd749-6ad3-74e3-bcac-1e072dbe2940" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery_019fd749-6ad3-703e-9d27-f8294b88a885" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FinancingReceivableCreditLossExpenseReversalExcludingHeldToMaturitySecurities_019fd749-6ad3-73da-83da-8895378bcdbc" xlink:href="onb-20260930.xsd#onb_FinancingReceivableCreditLossExpenseReversalExcludingHeldToMaturitySecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_019fd749-6ad3-74e3-bcac-1e072dbe2940" xlink:to="loc_onb_FinancingReceivableCreditLossExpenseReversalExcludingHeldToMaturitySecurities_019fd749-6ad3-73da-83da-8895378bcdbc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019fd749-6ad3-7434-9fb3-08205f2a1f85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofAllowanceforCreditLossesonUnfundedLoanCommitmentsDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofAllowanceforCreditLossesonUnfundedLoanCommitmentsDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofAllowanceforCreditLossesonUnfundedLoanCommitmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_019fd749-6ad3-7436-a6ac-24b8843ef374" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_019fd749-6ad3-70ea-a10c-c45c031d3c2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_019fd749-6ad3-7436-a6ac-24b8843ef374" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_019fd749-6ad3-70ea-a10c-c45c031d3c2a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019fd749-6ad3-74cf-8fc5-ba0646495e78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_019fd749-6ad3-70ea-a10c-c45c031d3c2a" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019fd749-6ad3-74cf-8fc5-ba0646495e78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-74cf-8fc5-ba0646495e78_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019fd749-6ad3-74cf-8fc5-ba0646495e78" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-74cf-8fc5-ba0646495e78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f31-8908-2c71b72c6484" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019fd749-6ad3-74cf-8fc5-ba0646495e78" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f31-8908-2c71b72c6484" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnfundedLoanCommitmentMember_019fd749-6ad3-71c3-b1cb-31d5c81e4b4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnfundedLoanCommitmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f31-8908-2c71b72c6484" xlink:to="loc_us-gaap_UnfundedLoanCommitmentMember_019fd749-6ad3-71c3-b1cb-31d5c81e4b4b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffBalanceSheetCreditLossLiabilityRollforward_019fd749-6ad3-70c1-8225-858a8443ba52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffBalanceSheetCreditLossLiabilityRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_019fd749-6ad3-7436-a6ac-24b8843ef374" xlink:to="loc_us-gaap_OffBalanceSheetCreditLossLiabilityRollforward_019fd749-6ad3-70c1-8225-858a8443ba52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffBalanceSheetCreditLossLiability_019fd749-6ad3-7041-a525-913a1a23c54a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffBalanceSheetCreditLossLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffBalanceSheetCreditLossLiabilityRollforward_019fd749-6ad3-70c1-8225-858a8443ba52" xlink:to="loc_us-gaap_OffBalanceSheetCreditLossLiability_019fd749-6ad3-7041-a525-913a1a23c54a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OffBalanceSheetCreditLossLiabilityAcquiredLoans_019fd749-6ad3-7cba-8bd6-4df0504af7f1" xlink:href="onb-20260930.xsd#onb_OffBalanceSheetCreditLossLiabilityAcquiredLoans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffBalanceSheetCreditLossLiabilityRollforward_019fd749-6ad3-70c1-8225-858a8443ba52" xlink:to="loc_onb_OffBalanceSheetCreditLossLiabilityAcquiredLoans_019fd749-6ad3-7cba-8bd6-4df0504af7f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal_019fd749-6ad3-7351-86f5-e754f06c0724" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OffBalanceSheetCreditLossLiabilityRollforward_019fd749-6ad3-70c1-8225-858a8443ba52" xlink:to="loc_us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal_019fd749-6ad3-7351-86f5-e754f06c0724" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffBalanceSheetCreditLossLiability_019fd749-6ad3-75ca-bfe8-748e33c7949a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OffBalanceSheetCreditLossLiability"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofRiskRatingandPaymentPerformanceDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofRiskRatingandPaymentPerformanceDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofRiskRatingandPaymentPerformanceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019fd749-6ad3-70ba-ae7e-af4568c40dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019fd749-6ad3-70ba-ae7e-af4568c40dc6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentAxis_019fd749-6ad3-7f94-8a34-e504d39d0e68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019fd749-6ad3-70ba-ae7e-af4568c40dc6" xlink:to="loc_us-gaap_InternalCreditAssessmentAxis_019fd749-6ad3-7f94-8a34-e504d39d0e68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-7f94-8a34-e504d39d0e68_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_019fd749-6ad3-7f94-8a34-e504d39d0e68" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-7f94-8a34-e504d39d0e68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-74ce-80bf-87d12840eb58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_019fd749-6ad3-7f94-8a34-e504d39d0e68" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-74ce-80bf-87d12840eb58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PassMember_019fd749-6ad3-7edf-a6a0-0c654aebb030" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PassMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-74ce-80bf-87d12840eb58" xlink:to="loc_us-gaap_PassMember_019fd749-6ad3-7edf-a6a0-0c654aebb030" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SpecialMentionMember_019fd749-6ad3-7a7f-a85f-6bcf638e232e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SpecialMentionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-74ce-80bf-87d12840eb58" xlink:to="loc_us-gaap_SpecialMentionMember_019fd749-6ad3-7a7f-a85f-6bcf638e232e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubstandardMember_019fd749-6ad3-7f49-ac94-b5f9af03a010" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubstandardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-74ce-80bf-87d12840eb58" xlink:to="loc_us-gaap_SubstandardMember_019fd749-6ad3-7f49-ac94-b5f9af03a010" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_NonAccrualMember_019fd749-6ad3-711b-9a14-9e8dd5708c21" xlink:href="onb-20260930.xsd#onb_NonAccrualMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-74ce-80bf-87d12840eb58" xlink:to="loc_onb_NonAccrualMember_019fd749-6ad3-711b-9a14-9e8dd5708c21" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DoubtfulMember_019fd749-6ad3-77e5-a429-a057c9dad6f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DoubtfulMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_019fd749-6ad3-74ce-80bf-87d12840eb58" xlink:to="loc_us-gaap_DoubtfulMember_019fd749-6ad3-77e5-a429-a057c9dad6f7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7201-a1c9-7096f14a1996" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019fd749-6ad3-70ba-ae7e-af4568c40dc6" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7201-a1c9-7096f14a1996" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7201-a1c9-7096f14a1996_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7201-a1c9-7096f14a1996" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7201-a1c9-7096f14a1996_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7201-a1c9-7096f14a1996" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-77a3-9205-e55f9047add6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-77a3-9205-e55f9047add6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-77f8-b059-6fed9a327c62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-77f8-b059-6fed9a327c62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7909-8bd6-7883f39f3156" xlink:href="onb-20260930.xsd#onb_BusinessBankingCreditCenterPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:to="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7909-8bd6-7883f39f3156" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-73be-8d4b-42ded3d5e3a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-73be-8d4b-42ded3d5e3a3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-78d2-8b5e-2726b28a30e4" xlink:href="onb-20260930.xsd#onb_IndirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:to="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-78d2-8b5e-2726b28a30e4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-7d27-b933-58789ddcade7" xlink:href="onb-20260930.xsd#onb_DirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:to="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-7d27-b933-58789ddcade7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-72f8-beb0-8b5a50621504" xlink:href="onb-20260930.xsd#onb_HomeEquityPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:to="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-72f8-beb0-8b5a50621504" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherConsumerSegmentMember_01a157fd-bb55-7bd6-b020-a0a4a43ec794" xlink:href="onb-20260930.xsd#onb_OtherConsumerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7298-94eb-c4bb031cfb2e" xlink:to="loc_onb_OtherConsumerSegmentMember_01a157fd-bb55-7bd6-b020-a0a4a43ec794" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentPerformanceStatusAxis_019fd749-6ad3-7a14-8f48-5942a34267e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentPerformanceStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019fd749-6ad3-70ba-ae7e-af4568c40dc6" xlink:to="loc_us-gaap_FinancialInstrumentPerformanceStatusAxis_019fd749-6ad3-7a14-8f48-5942a34267e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentPerformanceStatusDomain_019fd749-6ad3-7a14-8f48-5942a34267e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentPerformanceStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentPerformanceStatusAxis_019fd749-6ad3-7a14-8f48-5942a34267e1" xlink:to="loc_us-gaap_FinancialInstrumentPerformanceStatusDomain_019fd749-6ad3-7a14-8f48-5942a34267e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentPerformanceStatusDomain_019fd749-6ad3-773d-b1c0-34752778d3fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentPerformanceStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentPerformanceStatusAxis_019fd749-6ad3-7a14-8f48-5942a34267e1" xlink:to="loc_us-gaap_FinancialInstrumentPerformanceStatusDomain_019fd749-6ad3-773d-b1c0-34752778d3fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformingFinancingReceivableMember_019fd749-6ad3-793b-b772-f8b0b212a9f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformingFinancingReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentPerformanceStatusDomain_019fd749-6ad3-773d-b1c0-34752778d3fe" xlink:to="loc_us-gaap_PerformingFinancingReceivableMember_019fd749-6ad3-793b-b772-f8b0b212a9f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonperformingFinancingReceivableMember_019fd749-6ad3-74b7-a005-f30eae836ea8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonperformingFinancingReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentPerformanceStatusDomain_019fd749-6ad3-773d-b1c0-34752778d3fe" xlink:to="loc_us-gaap_NonperformingFinancingReceivableMember_019fd749-6ad3-74b7-a005-f30eae836ea8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-781a-bbee-356344a3bbfa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_019fd749-6ad3-70ba-ae7e-af4568c40dc6" xlink:to="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-781a-bbee-356344a3bbfa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-781a-bbee-356344a3bbfa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-781a-bbee-356344a3bbfa" xlink:to="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-781a-bbee-356344a3bbfa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-762f-ab55-9fa93d837cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-781a-bbee-356344a3bbfa" xlink:to="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-762f-ab55-9fa93d837cde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_SegmentPortfolioReclassificationAdjustedBalanceMember_019fd749-6ad3-7ba9-bc07-658e5853cbbe" xlink:href="onb-20260930.xsd#onb_SegmentPortfolioReclassificationAdjustedBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-762f-ab55-9fa93d837cde" xlink:to="loc_onb_SegmentPortfolioReclassificationAdjustedBalanceMember_019fd749-6ad3-7ba9-bc07-658e5853cbbe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear_019fd749-6ad3-7bcf-87c6-5f0f4093daf0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear_019fd749-6ad3-7bcf-87c6-5f0f4093daf0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear_019fd749-6ad3-7e37-a577-bc7e81127304" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear_019fd749-6ad3-7e37-a577-bc7e81127304" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear_019fd749-6ad3-7778-a278-e4487212ceb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear_019fd749-6ad3-7778-a278-e4487212ceb9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear_019fd749-6ad3-79db-9975-673d70ff1678" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear_019fd749-6ad3-79db-9975-673d70ff1678" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear_019fd749-6ad3-728d-9d82-2c222eca4bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear_019fd749-6ad3-728d-9d82-2c222eca4bbf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear_019fd749-6ad3-71a2-a4d7-4df5aa50b6b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear_019fd749-6ad3-71a2-a4d7-4df5aa50b6b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolving_019fd749-6ad3-7ae2-812f-f98f8bb7cf9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolving"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolving_019fd749-6ad3-7ae2-812f-f98f8bb7cf9e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan_019fd749-6ad3-731b-becd-fe3eeec8cac9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan_019fd749-6ad3-731b-becd-fe3eeec8cac9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7077-afab-5bb920b32c7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7077-afab-5bb920b32c7e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_019fd749-6ad3-722d-857d-81b43331e1af" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff_019fd749-6ad3-75d6-9f98-cd5d79845582" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff_019fd749-6ad3-75d6-9f98-cd5d79845582" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-7f4a-9c50-18ab884cb427" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-7f4a-9c50-18ab884cb427" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-79de-a849-76c9cb0dceb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-79de-a849-76c9cb0dceb7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-76b8-8a8b-d0eb89b3dc77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-76b8-8a8b-d0eb89b3dc77" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-73f0-9cb8-16c3889480b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-73f0-9cb8-16c3889480b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-7f0c-91f2-b10bd1a98a1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff_019fd749-6ad3-7f0c-91f2-b10bd1a98a1d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FinancingReceivableExcludingAccruedInterestRevolvingOriginatedCurrentFiscalYearWriteoff_019fd749-6ad3-76d4-9cc2-68db25b8da5d" xlink:href="onb-20260930.xsd#onb_FinancingReceivableExcludingAccruedInterestRevolvingOriginatedCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:to="loc_onb_FinancingReceivableExcludingAccruedInterestRevolvingOriginatedCurrentFiscalYearWriteoff_019fd749-6ad3-76d4-9cc2-68db25b8da5d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019fd749-6ad3-712c-b080-335c2fb77db5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffByOriginationYearAbstract_019fd749-6ad3-7419-850a-ca7717c94609" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019fd749-6ad3-712c-b080-335c2fb77db5" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofPastDueLoansDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofPastDueLoansDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofPastDueLoansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019fd749-6ad3-7d0e-8506-66b1513ffe85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019fd749-6ad3-7fe8-809a-b8d94595e702" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019fd749-6ad3-7d0e-8506-66b1513ffe85" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019fd749-6ad3-7fe8-809a-b8d94595e702" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_019fd749-6ad3-707b-9089-f9d0ec77f921" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019fd749-6ad3-7fe8-809a-b8d94595e702" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_019fd749-6ad3-707b-9089-f9d0ec77f921" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-707b-9089-f9d0ec77f921_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_019fd749-6ad3-707b-9089-f9d0ec77f921" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-707b-9089-f9d0ec77f921_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-7a39-b7d1-dc02f21a569f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_019fd749-6ad3-707b-9089-f9d0ec77f921" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-7a39-b7d1-dc02f21a569f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetPastDueMember_019fd749-6ad3-7c2d-9e44-ccea9cd16031" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialAssetPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-7a39-b7d1-dc02f21a569f" xlink:to="loc_us-gaap_FinancialAssetPastDueMember_019fd749-6ad3-7c2d-9e44-ccea9cd16031" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables30To59DaysPastDueMember_019fd749-6ad3-7c03-9b42-6cc01f58cef3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivables30To59DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialAssetPastDueMember_019fd749-6ad3-7c2d-9e44-ccea9cd16031" xlink:to="loc_us-gaap_FinancingReceivables30To59DaysPastDueMember_019fd749-6ad3-7c03-9b42-6cc01f58cef3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_019fd749-6ad3-76ce-a887-d13d4aa4e522" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialAssetPastDueMember_019fd749-6ad3-7c2d-9e44-ccea9cd16031" xlink:to="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_019fd749-6ad3-76ce-a887-d13d4aa4e522" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_019fd749-6ad3-7a8b-aaeb-26051671c723" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialAssetPastDueMember_019fd749-6ad3-7c2d-9e44-ccea9cd16031" xlink:to="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_019fd749-6ad3-7a8b-aaeb-26051671c723" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetNotPastDueMember_019fd749-6ad3-7d14-8fd1-80201fc70f91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialAssetNotPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-7a39-b7d1-dc02f21a569f" xlink:to="loc_us-gaap_FinancialAssetNotPastDueMember_019fd749-6ad3-7d14-8fd1-80201fc70f91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-70d3-bf7a-0bc1ddb25812" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019fd749-6ad3-7fe8-809a-b8d94595e702" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-70d3-bf7a-0bc1ddb25812" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-70d3-bf7a-0bc1ddb25812_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-70d3-bf7a-0bc1ddb25812" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-70d3-bf7a-0bc1ddb25812_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-70d3-bf7a-0bc1ddb25812" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-7bd2-ab6c-c82dca6984d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-7bd2-ab6c-c82dca6984d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-721a-a24e-b1992768c908" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-721a-a24e-b1992768c908" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-78a8-a748-9f0a95263bd8" xlink:href="onb-20260930.xsd#onb_BusinessBankingCreditCenterPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:to="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-78a8-a748-9f0a95263bd8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-792d-a566-0e75f9429499" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-792d-a566-0e75f9429499" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7265-8f8a-785216f463d6" xlink:href="onb-20260930.xsd#onb_IndirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:to="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7265-8f8a-785216f463d6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-7419-aa42-9a99b9ea4a7a" xlink:href="onb-20260930.xsd#onb_DirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:to="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-7419-aa42-9a99b9ea4a7a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-7af9-8d6d-45c837802c40" xlink:href="onb-20260930.xsd#onb_HomeEquityPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:to="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-7af9-8d6d-45c837802c40" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherConsumerSegmentMember_01a157ff-e32e-7e03-b037-7aff10388236" xlink:href="onb-20260930.xsd#onb_OtherConsumerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7282-bdd9-43f969a513b4" xlink:to="loc_onb_OtherConsumerSegmentMember_01a157ff-e32e-7e03-b037-7aff10388236" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-7d28-b064-447418fb2cc9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019fd749-6ad3-7fe8-809a-b8d94595e702" xlink:to="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-7d28-b064-447418fb2cc9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7d28-b064-447418fb2cc9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-7d28-b064-447418fb2cc9" xlink:to="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7d28-b064-447418fb2cc9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7142-b176-ede718af3071" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationTypeAxis_019fd749-6ad3-7d28-b064-447418fb2cc9" xlink:to="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7142-b176-ede718af3071" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_SegmentPortfolioReclassificationAdjustedBalanceMember_019fd749-6ad3-7c36-aba1-49563cc47ec6" xlink:href="onb-20260930.xsd#onb_SegmentPortfolioReclassificationAdjustedBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationTypeDomain_019fd749-6ad3-7142-b176-ede718af3071" xlink:to="loc_onb_SegmentPortfolioReclassificationAdjustedBalanceMember_019fd749-6ad3-7c36-aba1-49563cc47ec6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7664-90f0-8b477ef244e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019fd749-6ad3-7d0e-8506-66b1513ffe85" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7664-90f0-8b477ef244e8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofNonaccrualLoansDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofNonaccrualLoansDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofNonaccrualLoansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_019fd749-6ad3-7f84-ab28-139961cda2b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableNonaccrualStatusLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableNonaccrualTable_019fd749-6ad3-78bc-8264-50073b9b704f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableNonaccrualTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_019fd749-6ad3-7f84-ab28-139961cda2b6" xlink:to="loc_us-gaap_FinancingReceivableNonaccrualTable_019fd749-6ad3-78bc-8264-50073b9b704f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7761-94c1-91fe658a4bf9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualTable_019fd749-6ad3-78bc-8264-50073b9b704f" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7761-94c1-91fe658a4bf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7761-94c1-91fe658a4bf9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7761-94c1-91fe658a4bf9" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7761-94c1-91fe658a4bf9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7761-94c1-91fe658a4bf9" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-71ad-8c6f-229d304ab535" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-71ad-8c6f-229d304ab535" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7897-ad34-78409fc22be7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7897-ad34-78409fc22be7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7dd7-841a-4dbea6d4a720" xlink:href="onb-20260930.xsd#onb_BusinessBankingCreditCenterPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:to="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7dd7-841a-4dbea6d4a720" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-7c20-8348-bee78ea14825" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-7c20-8348-bee78ea14825" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7cc5-af6d-7b17cc42ffe7" xlink:href="onb-20260930.xsd#onb_IndirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:to="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7cc5-af6d-7b17cc42ffe7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-70fb-b7c0-7c3fed24f0e9" xlink:href="onb-20260930.xsd#onb_DirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:to="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-70fb-b7c0-7c3fed24f0e9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-7c43-887f-bf7360f982ec" xlink:href="onb-20260930.xsd#onb_HomeEquityPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:to="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-7c43-887f-bf7360f982ec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherConsumerSegmentMember_01a15800-6506-7ae5-af85-9b166dbe3488" xlink:href="onb-20260930.xsd#onb_OtherConsumerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b6d-9323-86f071f17421" xlink:to="loc_onb_OtherConsumerSegmentMember_01a15800-6506-7ae5-af85-9b166dbe3488" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_019fd749-6ad3-7149-ba48-326b7a2e0ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_019fd749-6ad3-7f84-ab28-139961cda2b6" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_019fd749-6ad3-7149-ba48-326b7a2e0ec8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableNonaccrualNoAllowance_019fd749-6ad3-7e0a-8f34-f554339158e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableNonaccrualNoAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_019fd749-6ad3-7f84-ab28-139961cda2b6" xlink:to="loc_us-gaap_FinancingReceivableNonaccrualNoAllowance_019fd749-6ad3-7e0a-8f34-f554339158e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_019fd749-6ad3-7785-a835-cfca6e897ccb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_019fd749-6ad3-7f84-ab28-139961cda2b6" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_019fd749-6ad3-7785-a835-cfca6e897ccb" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofTypesofCollateralDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofTypesofCollateralDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofTypesofCollateralDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-797f-a989-c10d41292e29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-75c7-8507-90ec2b053d27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-797f-a989-c10d41292e29" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-75c7-8507-90ec2b053d27" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7417-947d-b35cd3165ffe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-75c7-8507-90ec2b053d27" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7417-947d-b35cd3165ffe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7417-947d-b35cd3165ffe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7417-947d-b35cd3165ffe" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7417-947d-b35cd3165ffe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7417-947d-b35cd3165ffe" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-78d4-86e0-44056163daa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-78d4-86e0-44056163daa8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7e37-a03f-e1f95028fba9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7e37-a03f-e1f95028fba9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7492-b5a5-af1b597e94ad" xlink:href="onb-20260930.xsd#onb_BusinessBankingCreditCenterPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:to="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_019fd749-6ad3-7492-b5a5-af1b597e94ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-7d70-a6bc-75c41a0e174d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6ad3-7d70-a6bc-75c41a0e174d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7618-8bef-d8ae9456f250" xlink:href="onb-20260930.xsd#onb_IndirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:to="loc_onb_IndirectPortfolioSegmentMember_019fd749-6ad3-7618-8bef-d8ae9456f250" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-783d-8adc-cfce6de2532b" xlink:href="onb-20260930.xsd#onb_DirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:to="loc_onb_DirectPortfolioSegmentMember_019fd749-6ad3-783d-8adc-cfce6de2532b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-7c28-8334-a00b66d2c547" xlink:href="onb-20260930.xsd#onb_HomeEquityPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:to="loc_onb_HomeEquityPortfolioSegmentMember_019fd749-6ad3-7c28-8334-a00b66d2c547" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherConsumerSegmentMember_01a15801-7799-7ae1-a81c-aeaa3a1d4f31" xlink:href="onb-20260930.xsd#onb_OtherConsumerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7896-b9fa-2dcf31dd4383" xlink:to="loc_onb_OtherConsumerSegmentMember_01a15801-7799-7ae1-a81c-aeaa3a1d4f31" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019fd749-6ad3-7c68-ac43-93d161ef441e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-75c7-8507-90ec2b053d27" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019fd749-6ad3-7c68-ac43-93d161ef441e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7c68-ac43-93d161ef441e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019fd749-6ad3-7c68-ac43-93d161ef441e" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7c68-ac43-93d161ef441e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f11-bd09-07c3e310e340" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019fd749-6ad3-7c68-ac43-93d161ef441e" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f11-bd09-07c3e310e340" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateMember_019fd749-6ad3-75d5-a080-0035a257aec5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f11-bd09-07c3e310e340" xlink:to="loc_us-gaap_RealEstateMember_019fd749-6ad3-75d5-a080-0035a257aec5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BlanketLienCollateralMember_019fd749-6ad3-7fca-a557-6cd22d46805b" xlink:href="onb-20260930.xsd#onb_BlanketLienCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f11-bd09-07c3e310e340" xlink:to="loc_onb_BlanketLienCollateralMember_019fd749-6ad3-7fca-a557-6cd22d46805b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_InvestmentSecuritiesAndCashCollateralMember_019fd749-6ad3-7d80-8ace-83e3c5de3bc1" xlink:href="onb-20260930.xsd#onb_InvestmentSecuritiesAndCashCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f11-bd09-07c3e310e340" xlink:to="loc_onb_InvestmentSecuritiesAndCashCollateralMember_019fd749-6ad3-7d80-8ace-83e3c5de3bc1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AutomobilesMember_019fd749-6ad3-7b7e-8e12-f3e8ff49ae41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AutomobilesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f11-bd09-07c3e310e340" xlink:to="loc_us-gaap_AutomobilesMember_019fd749-6ad3-7b7e-8e12-f3e8ff49ae41" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherCollateralMember_019fd749-6ad3-79d0-aae3-742ffad3e475" xlink:href="onb-20260930.xsd#onb_OtherCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019fd749-6ad3-7f11-bd09-07c3e310e340" xlink:to="loc_onb_OtherCollateralMember_019fd749-6ad3-79d0-aae3-742ffad3e475" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7888-8d3b-7fc49eab47b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-797f-a989-c10d41292e29" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019fd749-6ad3-7888-8d3b-7fc49eab47b1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofAmortizedCostBasisofLoanswithModificationsDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofAmortizedCostBasisofLoanswithModificationsDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofAmortizedCostBasisofLoanswithModificationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7de3-bca4-6c3ce7e3501e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-70f3-84ac-fb9423140879" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7de3-bca4-6c3ce7e3501e" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-70f3-84ac-fb9423140879" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7b69-bda2-924bc3339c66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-70f3-84ac-fb9423140879" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7b69-bda2-924bc3339c66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b69-bda2-924bc3339c66_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7b69-bda2-924bc3339c66" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7b69-bda2-924bc3339c66_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7b69-bda2-924bc3339c66" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-7b27-8d2b-eccc1976073f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-7b27-8d2b-eccc1976073f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-79d8-94c2-14e87dad7f0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-79d8-94c2-14e87dad7f0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_01a15a8f-6154-7468-bd98-58c0e903914e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_01a15a8f-6154-7468-bd98-58c0e903914e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_IndirectPortfolioSegmentMember_01a15a8f-6154-70e8-b718-51277f93fbc2" xlink:href="onb-20260930.xsd#onb_IndirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:to="loc_onb_IndirectPortfolioSegmentMember_01a15a8f-6154-70e8-b718-51277f93fbc2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_HomeEquityPortfolioSegmentMember_01a15a8f-6154-795e-83af-d967f1ff7b8b" xlink:href="onb-20260930.xsd#onb_HomeEquityPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:to="loc_onb_HomeEquityPortfolioSegmentMember_01a15a8f-6154-795e-83af-d967f1ff7b8b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherConsumerSegmentMember_01a15a8f-6154-75e1-b6de-611e2027e78e" xlink:href="onb-20260930.xsd#onb_OtherConsumerSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:to="loc_onb_OtherConsumerSegmentMember_01a15a8f-6154-75e1-b6de-611e2027e78e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_01a15a8f-6154-7c2d-9824-159971a320ca" xlink:href="onb-20260930.xsd#onb_BusinessBankingCreditCenterPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:to="loc_onb_BusinessBankingCreditCenterPortfolioSegmentMember_01a15a8f-6154-7c2d-9824-159971a320ca" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DirectPortfolioSegmentMember_01a15a8f-6154-76f9-ada4-f44cf2402a92" xlink:href="onb-20260930.xsd#onb_DirectPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-792b-90fc-e11e4d5a1338" xlink:to="loc_onb_DirectPortfolioSegmentMember_01a15a8f-6154-76f9-ada4-f44cf2402a92" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationAxis_019fd749-6ad3-78e1-b0b0-3f411a5ac978" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanRestructuringModificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-70f3-84ac-fb9423140879" xlink:to="loc_us-gaap_LoanRestructuringModificationAxis_019fd749-6ad3-78e1-b0b0-3f411a5ac978" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-78e1-b0b0-3f411a5ac978_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanRestructuringModificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LoanRestructuringModificationAxis_019fd749-6ad3-78e1-b0b0-3f411a5ac978" xlink:to="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-78e1-b0b0-3f411a5ac978_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-763a-86f0-3df1d5adefbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanRestructuringModificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LoanRestructuringModificationAxis_019fd749-6ad3-78e1-b0b0-3f411a5ac978" xlink:to="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-763a-86f0-3df1d5adefbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtendedMaturityMember_019fd749-6ad3-7825-b393-c9c2707be846" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtendedMaturityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-763a-86f0-3df1d5adefbd" xlink:to="loc_us-gaap_ExtendedMaturityMember_019fd749-6ad3-7825-b393-c9c2707be846" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentDeferralMember_019fd749-6ad3-7abc-9c49-9e45c44a84c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentDeferralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-763a-86f0-3df1d5adefbd" xlink:to="loc_us-gaap_PaymentDeferralMember_019fd749-6ad3-7abc-9c49-9e45c44a84c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateBelowMarketReductionMember_019fd749-6ad3-728b-ac09-05a5e4e0860f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateBelowMarketReductionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-763a-86f0-3df1d5adefbd" xlink:to="loc_us-gaap_InterestRateBelowMarketReductionMember_019fd749-6ad3-728b-ac09-05a5e4e0860f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_01a15a8f-6154-72d6-bc15-e6965e0ae7f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-70f3-84ac-fb9423140879" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_01a15a8f-6154-72d6-bc15-e6965e0ae7f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-72d6-bc15-e6965e0ae7f9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_01a15a8f-6154-72d6-bc15-e6965e0ae7f9" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-72d6-bc15-e6965e0ae7f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-7387-91dd-2552a58a4b8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_01a15a8f-6154-72d6-bc15-e6965e0ae7f9" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-7387-91dd-2552a58a4b8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateMember_01a15a8f-6154-71fc-95ee-bfee03eed042" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-7387-91dd-2552a58a4b8a" xlink:to="loc_us-gaap_RealEstateMember_01a15a8f-6154-71fc-95ee-bfee03eed042" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BlanketLienCollateralMember_01a15a8f-6154-7269-be62-2df0a27731e8" xlink:href="onb-20260930.xsd#onb_BlanketLienCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-7387-91dd-2552a58a4b8a" xlink:to="loc_onb_BlanketLienCollateralMember_01a15a8f-6154-7269-be62-2df0a27731e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_InvestmentSecuritiesAndCashCollateralMember_01a15a8f-6154-7f30-b488-06ef5b3eff98" xlink:href="onb-20260930.xsd#onb_InvestmentSecuritiesAndCashCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-7387-91dd-2552a58a4b8a" xlink:to="loc_onb_InvestmentSecuritiesAndCashCollateralMember_01a15a8f-6154-7f30-b488-06ef5b3eff98" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AutomobilesMember_01a15a8f-6154-7a80-b4dc-ec9f77154a19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AutomobilesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-7387-91dd-2552a58a4b8a" xlink:to="loc_us-gaap_AutomobilesMember_01a15a8f-6154-7a80-b4dc-ec9f77154a19" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherCollateralMember_01a15a8f-6154-7f11-918c-1f2728a5e6d4" xlink:href="onb-20260930.xsd#onb_OtherCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_01a15a8f-6154-7387-91dd-2552a58a4b8a" xlink:to="loc_onb_OtherCollateralMember_01a15a8f-6154-7f11-918c-1f2728a5e6d4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_01a15a8f-6154-7817-aa21-6ef062f6cb25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7de3-bca4-6c3ce7e3501e" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_01a15a8f-6154-7817-aa21-6ef062f6cb25" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod_019fd749-6ad3-7a60-8f32-e47274e53fb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7de3-bca4-6c3ce7e3501e" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod_019fd749-6ad3-7a60-8f32-e47274e53fb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent_019fd749-6ad3-700e-8ec7-9ff552e68cdd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7de3-bca4-6c3ce7e3501e" xlink:to="loc_us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent_019fd749-6ad3-700e-8ec7-9ff552e68cdd" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofNatureofLoanModificationstoBorrowersExperiencingFinancialDifficultyDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofNatureofLoanModificationstoBorrowersExperiencingFinancialDifficultyDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofNatureofLoanModificationstoBorrowersExperiencingFinancialDifficultyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e5a-84b5-5225d6cb8ef3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7b04-83e5-ed2c78af1399" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e5a-84b5-5225d6cb8ef3" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7b04-83e5-ed2c78af1399" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7a5d-9eed-83d1bb6cd166" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7b04-83e5-ed2c78af1399" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7a5d-9eed-83d1bb6cd166" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7a5d-9eed-83d1bb6cd166_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7a5d-9eed-83d1bb6cd166" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7a5d-9eed-83d1bb6cd166_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7936-85b1-da44c37b7029" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7a5d-9eed-83d1bb6cd166" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7936-85b1-da44c37b7029" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-75c0-a727-9e29dd48423d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7936-85b1-da44c37b7029" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-75c0-a727-9e29dd48423d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-793b-b457-3f118dd17e43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7936-85b1-da44c37b7029" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-793b-b457-3f118dd17e43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationAxis_019fd749-6ad3-73fe-b7c7-44e149fbb111" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanRestructuringModificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7b04-83e5-ed2c78af1399" xlink:to="loc_us-gaap_LoanRestructuringModificationAxis_019fd749-6ad3-73fe-b7c7-44e149fbb111" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-73fe-b7c7-44e149fbb111_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanRestructuringModificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LoanRestructuringModificationAxis_019fd749-6ad3-73fe-b7c7-44e149fbb111" xlink:to="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-73fe-b7c7-44e149fbb111_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-7a22-8205-67619b068f4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoanRestructuringModificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LoanRestructuringModificationAxis_019fd749-6ad3-73fe-b7c7-44e149fbb111" xlink:to="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-7a22-8205-67619b068f4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtendedMaturityMember_019fd749-6ad3-7df3-8395-5bc798ad7e5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtendedMaturityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-7a22-8205-67619b068f4e" xlink:to="loc_us-gaap_ExtendedMaturityMember_019fd749-6ad3-7df3-8395-5bc798ad7e5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentDeferralMember_019fd749-6ad3-775b-bf4c-62985f21e371" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentDeferralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_019fd749-6ad3-7a22-8205-67619b068f4e" xlink:to="loc_us-gaap_PaymentDeferralMember_019fd749-6ad3-775b-bf4c-62985f21e371" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification_019fd749-6ad3-7eac-8c9e-ff9c131f2473" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e5a-84b5-5225d6cb8ef3" xlink:to="loc_us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification_019fd749-6ad3-7eac-8c9e-ff9c131f2473" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModifiedPaymentDeferralPeriod_019fd749-6ad3-7906-b784-1f691671f09e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableModifiedPaymentDeferralPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e5a-84b5-5225d6cb8ef3" xlink:to="loc_us-gaap_FinancingReceivableModifiedPaymentDeferralPeriod_019fd749-6ad3-7906-b784-1f691671f09e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModifiedWeightedAverageInterestRateDecreaseFromModification_019fd749-6ad3-7849-be98-4d849be795bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableModifiedWeightedAverageInterestRateDecreaseFromModification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e5a-84b5-5225d6cb8ef3" xlink:to="loc_us-gaap_FinancingReceivableModifiedWeightedAverageInterestRateDecreaseFromModification_019fd749-6ad3-7849-be98-4d849be795bb" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofMonitorsthePerformanceofLoanModificationstoBorrowersExperiencingFinancialDifficultytoUnderstandtheEffectivenessofitsModificationEffortsDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofMonitorsthePerformanceofLoanModificationstoBorrowersExperiencingFinancialDifficultytoUnderstandtheEffectivenessofitsModificationEffortsDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofMonitorsthePerformanceofLoanModificationstoBorrowersExperiencingFinancialDifficultytoUnderstandtheEffectivenessofitsModificationEffortsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-74ac-b671-7643acb8e228" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7d37-bb7f-bb2fad730c08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-74ac-b671-7643acb8e228" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7d37-bb7f-bb2fad730c08" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7952-9d2d-9a7d0c9f7192" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7d37-bb7f-bb2fad730c08" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7952-9d2d-9a7d0c9f7192" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7952-9d2d-9a7d0c9f7192_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7952-9d2d-9a7d0c9f7192" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7952-9d2d-9a7d0c9f7192_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7975-8371-c6f0197cebd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6ad3-7952-9d2d-9a7d0c9f7192" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7975-8371-c6f0197cebd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-777e-bd84-b493998d2534" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7975-8371-c6f0197cebd1" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6ad3-777e-bd84-b493998d2534" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7b42-a635-79ac84d5c03f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6ad3-7975-8371-c6f0197cebd1" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6ad3-7b42-a635-79ac84d5c03f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_019fd749-6ad3-77b4-b996-a7ab5c0a2afa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-7d37-bb7f-bb2fad730c08" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_019fd749-6ad3-77b4-b996-a7ab5c0a2afa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-77b4-b996-a7ab5c0a2afa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_019fd749-6ad3-77b4-b996-a7ab5c0a2afa" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-77b4-b996-a7ab5c0a2afa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-730a-8d8c-316998d4ca07" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_019fd749-6ad3-77b4-b996-a7ab5c0a2afa" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-730a-8d8c-316998d4ca07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables30To59DaysPastDueMember_019fd749-6ad3-7d90-a181-1aae37c83cd8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivables30To59DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-730a-8d8c-316998d4ca07" xlink:to="loc_us-gaap_FinancingReceivables30To59DaysPastDueMember_019fd749-6ad3-7d90-a181-1aae37c83cd8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_019fd749-6ad3-704f-a64e-5b9ab1f4feb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-730a-8d8c-316998d4ca07" xlink:to="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_019fd749-6ad3-704f-a64e-5b9ab1f4feb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_019fd749-6ad3-79b7-8a67-a446a9c6409c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-730a-8d8c-316998d4ca07" xlink:to="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_019fd749-6ad3-79b7-8a67-a446a9c6409c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetPastDueMember_019fd749-6ad3-7b5d-8f08-8343c00f746b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialAssetPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-730a-8d8c-316998d4ca07" xlink:to="loc_us-gaap_FinancialAssetPastDueMember_019fd749-6ad3-7b5d-8f08-8343c00f746b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetNotPastDueMember_019fd749-6ad3-7558-8d3a-3d84bf4e1be5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialAssetNotPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_019fd749-6ad3-730a-8d8c-316998d4ca07" xlink:to="loc_us-gaap_FinancialAssetNotPastDueMember_019fd749-6ad3-7558-8d3a-3d84bf4e1be5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod_019fd749-6ad3-7921-bbfa-3bb6c150f34f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-74ac-b671-7643acb8e228" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod_019fd749-6ad3-7921-bbfa-3bb6c150f34f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofPurchasedCreditDeterioratedLoansDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LOANSANDALLOWANCEFORCREDITLOSSESScheduleofPurchasedCreditDeterioratedLoansDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LOANSANDALLOWANCEFORCREDITLOSSESScheduleofPurchasedCreditDeterioratedLoansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e17-8e44-cb22b9813424" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-75ec-b58d-33714f634981" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e17-8e44-cb22b9813424" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-75ec-b58d-33714f634981" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7849-9bd9-008427d59028" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_019fd749-6ad3-75ec-b58d-33714f634981" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7849-9bd9-008427d59028" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7849-9bd9-008427d59028_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7849-9bd9-008427d59028" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7849-9bd9-008427d59028_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7e3c-84be-500a2651bd60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6ad3-7849-9bd9-008427d59028" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7e3c-84be-500a2651bd60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BremerMember_019fd749-6ad3-787c-8610-79c38c266424" xlink:href="onb-20260930.xsd#onb_BremerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6ad3-7e3c-84be-500a2651bd60" xlink:to="loc_onb_BremerMember_019fd749-6ad3-787c-8610-79c38c266424" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtPurchasePrice_019fd749-6ad3-7a13-a0dd-fb007b79315c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtPurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e17-8e44-cb22b9813424" xlink:to="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtPurchasePrice_019fd749-6ad3-7a13-a0dd-fb007b79315c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate_019fd749-6ad3-7b7e-a7cf-77b39802905c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e17-8e44-cb22b9813424" xlink:to="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate_019fd749-6ad3-7b7e-a7cf-77b39802905c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationDiscountPremium_019fd749-6ad3-755a-9f87-e420fd178697" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationDiscountPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e17-8e44-cb22b9813424" xlink:to="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationDiscountPremium_019fd749-6ad3-755a-9f87-e420fd178697" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtParValue_019fd749-6ad3-7d01-90ba-8792d460b8cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtParValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_019fd749-6ad3-7e17-8e44-cb22b9813424" xlink:to="loc_us-gaap_FinancingReceivablePurchasedWithCreditDeteriorationAmountAtParValue_019fd749-6ad3-7d01-90ba-8792d460b8cd" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/LEASESAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#LEASESAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/LEASESAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd749-6b74-73f1-9e6a-8d7b206413db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019fd749-6b74-752d-888f-026d58b45d3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd749-6b74-73f1-9e6a-8d7b206413db" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019fd749-6b74-752d-888f-026d58b45d3f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd749-6b74-74ce-99f6-fd4f3bdf074d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019fd749-6b74-752d-888f-026d58b45d3f" xlink:to="loc_srt_RangeAxis_019fd749-6b74-74ce-99f6-fd4f3bdf074d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-74ce-99f6-fd4f3bdf074d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd749-6b74-74ce-99f6-fd4f3bdf074d" xlink:to="loc_srt_RangeMember_019fd749-6b74-74ce-99f6-fd4f3bdf074d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-737e-929c-e9f8b4dc794e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd749-6b74-74ce-99f6-fd4f3bdf074d" xlink:to="loc_srt_RangeMember_019fd749-6b74-737e-929c-e9f8b4dc794e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd749-6b74-7d1a-8817-5884b136da40" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-737e-929c-e9f8b4dc794e" xlink:to="loc_srt_MinimumMember_019fd749-6b74-7d1a-8817-5884b136da40" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd749-6b74-7a41-bf3e-2ad705c34863" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-737e-929c-e9f8b4dc794e" xlink:to="loc_srt_MaximumMember_019fd749-6b74-7a41-bf3e-2ad705c34863" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019fd749-6b74-7d4d-b401-23ec9c42b15f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd749-6b74-73f1-9e6a-8d7b206413db" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019fd749-6b74-7d4d-b401-23ec9c42b15f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeFinanceLeaseTermOfContract1_019fd749-6b74-7758-8f61-02ab1ae8c6b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeFinanceLeaseTermOfContract1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019fd749-6b74-73f1-9e6a-8d7b206413db" xlink:to="loc_us-gaap_LesseeFinanceLeaseTermOfContract1_019fd749-6b74-7758-8f61-02ab1ae8c6b1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/GOODWILLANDOTHERINTANGIBLEASSETSAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#GOODWILLANDOTHERINTANGIBLEASSETSAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/GOODWILLANDOTHERINTANGIBLEASSETSAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_019fd749-6b74-7008-a558-d6dcbf5552e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_019fd749-6b74-7f46-9ca2-0541cb51bf68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_019fd749-6b74-7008-a558-d6dcbf5552e3" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_019fd749-6b74-7f46-9ca2-0541cb51bf68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd749-6b74-79e6-8b42-333dedc42107" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_019fd749-6b74-7f46-9ca2-0541cb51bf68" xlink:to="loc_srt_RangeAxis_019fd749-6b74-79e6-8b42-333dedc42107" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-79e6-8b42-333dedc42107_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd749-6b74-79e6-8b42-333dedc42107" xlink:to="loc_srt_RangeMember_019fd749-6b74-79e6-8b42-333dedc42107_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-7500-bfbf-f4c99055b094" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd749-6b74-79e6-8b42-333dedc42107" xlink:to="loc_srt_RangeMember_019fd749-6b74-7500-bfbf-f4c99055b094" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd749-6b74-750b-afb0-e67fe9955a4f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-7500-bfbf-f4c99055b094" xlink:to="loc_srt_MinimumMember_019fd749-6b74-750b-afb0-e67fe9955a4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd749-6b74-7932-b870-47ae2429bca2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-7500-bfbf-f4c99055b094" xlink:to="loc_srt_MaximumMember_019fd749-6b74-7932-b870-47ae2429bca2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6b74-74c2-b2be-962f49955421" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_019fd749-6b74-7f46-9ca2-0541cb51bf68" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6b74-74c2-b2be-962f49955421" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-74c2-b2be-962f49955421_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6b74-74c2-b2be-962f49955421" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-74c2-b2be-962f49955421_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-75e6-84a5-f664b380ed28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6b74-74c2-b2be-962f49955421" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-75e6-84a5-f664b380ed28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CoreDepositsMember_019fd749-6b74-7602-bc0d-16dd3d9bd836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CoreDepositsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-75e6-84a5-f664b380ed28" xlink:to="loc_us-gaap_CoreDepositsMember_019fd749-6b74-7602-bc0d-16dd3d9bd836" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_019fd749-6b74-7155-8fa7-25cbe254fa9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019fd749-6b74-7008-a558-d6dcbf5552e3" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_019fd749-6b74-7155-8fa7-25cbe254fa9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019fd749-6b74-73ed-aee4-3e0d25538aa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019fd749-6b74-7008-a558-d6dcbf5552e3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019fd749-6b74-73ed-aee4-3e0d25538aa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_019fd749-6b74-714e-b6f4-abcb5b40d9ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019fd749-6b74-7008-a558-d6dcbf5552e3" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_019fd749-6b74-714e-b6f4-abcb5b40d9ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019fd749-6b74-7fdf-bc6e-cb8cab827bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019fd749-6b74-7008-a558-d6dcbf5552e3" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019fd749-6b74-7fdf-bc6e-cb8cab827bf6" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/GOODWILLANDOTHERINTANGIBLEASSETSScheduleofGrossCarryingAmountsandAccumulatedAmortizationofOtherIntangibleAssetsDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#GOODWILLANDOTHERINTANGIBLEASSETSScheduleofGrossCarryingAmountsandAccumulatedAmortizationofOtherIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/GOODWILLANDOTHERINTANGIBLEASSETSScheduleofGrossCarryingAmountsandAccumulatedAmortizationofOtherIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd749-6b74-71a1-99b0-86892f53551b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd749-6b74-7515-8fe3-46ac6e1a17de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd749-6b74-71a1-99b0-86892f53551b" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd749-6b74-7515-8fe3-46ac6e1a17de" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6b74-7c68-b9c3-048708d37f9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019fd749-6b74-7515-8fe3-46ac6e1a17de" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6b74-7c68-b9c3-048708d37f9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-7c68-b9c3-048708d37f9c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6b74-7c68-b9c3-048708d37f9c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-7c68-b9c3-048708d37f9c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-72f5-aa2a-8aefebb59e66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd749-6b74-7c68-b9c3-048708d37f9c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-72f5-aa2a-8aefebb59e66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CoreDepositsMember_019fd749-6b74-72a9-bfc5-471a229c0fc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CoreDepositsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-72f5-aa2a-8aefebb59e66" xlink:to="loc_us-gaap_CoreDepositsMember_019fd749-6b74-72a9-bfc5-471a229c0fc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019fd749-6b74-7303-90ef-c1455176be2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd749-6b74-72f5-aa2a-8aefebb59e66" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019fd749-6b74-7303-90ef-c1455176be2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019fd749-6b74-7ec2-bc3c-6aa873682afc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd749-6b74-71a1-99b0-86892f53551b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019fd749-6b74-7ec2-bc3c-6aa873682afc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019fd749-6b74-7fc1-9bf8-0ad04d66357f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd749-6b74-71a1-99b0-86892f53551b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019fd749-6b74-7fc1-9bf8-0ad04d66357f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fd749-6b74-7350-b284-9f54f7661e6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019fd749-6b74-71a1-99b0-86892f53551b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019fd749-6b74-7350-b284-9f54f7661e6b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/QUALIFIEDAFFORDABLEHOUSINGPROJECTSANDOTHERTAXCREDITINVESTMENTSDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#QUALIFIEDAFFORDABLEHOUSINGPROJECTSANDOTHERTAXCREDITINVESTMENTSDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/QUALIFIEDAFFORDABLEHOUSINGPROJECTSANDOTHERTAXCREDITINVESTMENTSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SummaryOfInvestmentHoldingsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SummaryOfInvestmentHoldingsTable_019fd749-6b74-7bf9-9e4c-f1ed82ae7b4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SummaryOfInvestmentHoldingsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_SummaryOfInvestmentHoldingsTable_019fd749-6b74-7bf9-9e4c-f1ed82ae7b4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019fd749-6b74-7c12-922f-5cad319b3dab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsTable_019fd749-6b74-7bf9-9e4c-f1ed82ae7b4d" xlink:to="loc_us-gaap_InvestmentTypeAxis_019fd749-6b74-7c12-922f-5cad319b3dab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6b74-7c12-922f-5cad319b3dab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019fd749-6b74-7c12-922f-5cad319b3dab" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6b74-7c12-922f-5cad319b3dab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6b74-7041-84ee-4767f3950667" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019fd749-6b74-7c12-922f-5cad319b3dab" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6b74-7041-84ee-4767f3950667" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LowIncomeHousingTaxCreditsMember_019fd749-6b74-7a4a-98da-d3d334aded42" xlink:href="onb-20260930.xsd#onb_LowIncomeHousingTaxCreditsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6b74-7041-84ee-4767f3950667" xlink:to="loc_onb_LowIncomeHousingTaxCreditsMember_019fd749-6b74-7a4a-98da-d3d334aded42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FederalHistoricTaxCreditsMember_019fd749-6b74-760d-89de-0ccc3c3627a2" xlink:href="onb-20260930.xsd#onb_FederalHistoricTaxCreditsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6b74-7041-84ee-4767f3950667" xlink:to="loc_onb_FederalHistoricTaxCreditsMember_019fd749-6b74-760d-89de-0ccc3c3627a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_NewMarketsTaxCreditMember_019fd749-6b74-7b23-948b-d276352a2b0d" xlink:href="onb-20260930.xsd#onb_NewMarketsTaxCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6b74-7041-84ee-4767f3950667" xlink:to="loc_onb_NewMarketsTaxCreditMember_019fd749-6b74-7b23-948b-d276352a2b0d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RenewableEnergyProgramMember_019fd749-6b74-79f0-b91d-02a4ed9782ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RenewableEnergyProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fd749-6b74-7041-84ee-4767f3950667" xlink:to="loc_us-gaap_RenewableEnergyProgramMember_019fd749-6b74-79f0-b91d-02a4ed9782ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentProportionalAmortizationMethodElectedStatementOfFinancialPositionExtensibleEnumeration_019fd749-6b74-7e82-a57c-d2569347f604" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentProportionalAmortizationMethodElectedStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_InvestmentProportionalAmortizationMethodElectedStatementOfFinancialPositionExtensibleEnumeration_019fd749-6b74-7e82-a57c-d2569347f604" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestments_019fd749-6b74-7509-81a9-b629e5f635d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestments_019fd749-6b74-7509-81a9-b629e5f635d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_EquityMethodInvestmentQualifiedAffordableHousingProjectInvestments_019fd749-6b74-72f4-a890-aa557f265df6" xlink:href="onb-20260930.xsd#onb_EquityMethodInvestmentQualifiedAffordableHousingProjectInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_onb_EquityMethodInvestmentQualifiedAffordableHousingProjectInvestments_019fd749-6b74-72f4-a890-aa557f265df6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_InvestmentsInQualifiedAffordableHousingProjects_019fd749-6b74-7638-9247-0f965feca3dc" xlink:href="onb-20260930.xsd#onb_InvestmentsInQualifiedAffordableHousingProjects"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_onb_InvestmentsInQualifiedAffordableHousingProjects_019fd749-6b74-7638-9247-0f965feca3dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsCommitment_019fd749-6b74-7d54-bd47-46428582abdb" xlink:href="onb-20260930.xsd#onb_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_onb_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsCommitment_019fd749-6b74-7d54-bd47-46428582abdb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_EquityMethodQualifiedAffordableHousingProjectInvestmentsCommitment_019fd749-6b74-77e8-ab7b-c0c0dfc008f7" xlink:href="onb-20260930.xsd#onb_EquityMethodQualifiedAffordableHousingProjectInvestmentsCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_onb_EquityMethodQualifiedAffordableHousingProjectInvestmentsCommitment_019fd749-6b74-77e8-ab7b-c0c0dfc008f7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_QualifiedAffordableHousingProjectInvestmentsCommitment_019fd749-6b74-7840-a7ff-e97b97f1bdd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_QualifiedAffordableHousingProjectInvestmentsCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_QualifiedAffordableHousingProjectInvestmentsCommitment_019fd749-6b74-7840-a7ff-e97b97f1bdd0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization_019fd749-6b74-7b11-b944-9f29c48431a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization_019fd749-6b74-7b11-b944-9f29c48431a8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AffordableHousingTaxCreditsAndOtherTaxBenefitsAmount_019fd749-6b74-72af-97e5-48474877ae7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AffordableHousingTaxCreditsAndOtherTaxBenefitsAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_AffordableHousingTaxCreditsAndOtherTaxBenefitsAmount_019fd749-6b74-72af-97e5-48474877ae7a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentProgramProportionalAmortizationMethodAppliedIncomeTaxCreditAndOtherTaxBenefitAmortizationStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_019fd749-6b74-7860-b353-587e04d11f27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentProgramProportionalAmortizationMethodAppliedIncomeTaxCreditAndOtherTaxBenefitAmortizationStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_InvestmentProgramProportionalAmortizationMethodAppliedIncomeTaxCreditAndOtherTaxBenefitAmortizationStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_019fd749-6b74-7860-b353-587e04d11f27" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentProgramProportionalAmortizationMethodAppliedIncomeTaxCreditAndOtherTaxBenefitAmortizationStatementOfCashFlowsExtensibleEnumeration_019fd749-6b74-7735-b839-6e3495b5db89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentProgramProportionalAmortizationMethodAppliedIncomeTaxCreditAndOtherTaxBenefitAmortizationStatementOfCashFlowsExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_InvestmentProgramProportionalAmortizationMethodAppliedIncomeTaxCreditAndOtherTaxBenefitAmortizationStatementOfCashFlowsExtensibleEnumeration_019fd749-6b74-7735-b839-6e3495b5db89" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentProgramProportionalAmortizationMethodElectedIncomeTaxCreditAndOtherIncomeTaxBenefitBeforeAmortizationStatementOfCashFlowsExtensibleEnumeration_019fd749-6b74-7037-8e61-445679143aaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentProgramProportionalAmortizationMethodElectedIncomeTaxCreditAndOtherIncomeTaxBenefitBeforeAmortizationStatementOfCashFlowsExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_InvestmentProgramProportionalAmortizationMethodElectedIncomeTaxCreditAndOtherIncomeTaxBenefitBeforeAmortizationStatementOfCashFlowsExtensibleEnumeration_019fd749-6b74-7037-8e61-445679143aaf" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentProgramProportionalAmortizationMethodElectedIncomeTaxCreditAndOtherIncomeTaxBenefitBeforeAmortizationStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_019fd749-6b74-7d2a-9b6b-8b49533ba55c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentProgramProportionalAmortizationMethodElectedIncomeTaxCreditAndOtherIncomeTaxBenefitBeforeAmortizationStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfInvestmentHoldingsLineItems_019fd749-6b74-7f51-97ea-58a717a1a7de" xlink:to="loc_us-gaap_InvestmentProgramProportionalAmortizationMethodElectedIncomeTaxCreditAndOtherIncomeTaxBenefitBeforeAmortizationStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_019fd749-6b74-7d2a-9b6b-8b49533ba55c" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/SECURITIESSOLDUNDERAGREEMENTSTOREPURCHASEScheduleofRemainingContractualMaturityofSecuredBorrowingsandClassofCollateralPledgedDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#SECURITIESSOLDUNDERAGREEMENTSTOREPURCHASEScheduleofRemainingContractualMaturityofSecuredBorrowingsandClassofCollateralPledgedDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/SECURITIESSOLDUNDERAGREEMENTSTOREPURCHASEScheduleofRemainingContractualMaturityofSecuredBorrowingsandClassofCollateralPledgedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems_019fd749-6b74-7c70-84c9-acf7dfdfc085" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable_019fd749-6b74-781c-8128-a5ac2edf6150" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems_019fd749-6b74-7c70-84c9-acf7dfdfc085" xlink:to="loc_us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable_019fd749-6b74-781c-8128-a5ac2edf6150" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis_019fd749-6b74-75f0-ab91-91a2a611b872" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable_019fd749-6b74-781c-8128-a5ac2edf6150" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis_019fd749-6b74-75f0-ab91-91a2a611b872" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019fd749-6b74-75f0-ab91-91a2a611b872_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis_019fd749-6b74-75f0-ab91-91a2a611b872" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019fd749-6b74-75f0-ab91-91a2a611b872_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019fd749-6b74-7d7b-9cf2-992878bf9e67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis_019fd749-6b74-75f0-ab91-91a2a611b872" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019fd749-6b74-7d7b-9cf2-992878bf9e67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaturityOvernightMember_019fd749-6b74-720e-941e-b06f03ea394d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaturityOvernightMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019fd749-6b74-7d7b-9cf2-992878bf9e67" xlink:to="loc_us-gaap_MaturityOvernightMember_019fd749-6b74-720e-941e-b06f03ea394d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaturityUpTo30DaysMember_019fd749-6b74-70bc-8781-128b247ee2bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaturityUpTo30DaysMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019fd749-6b74-7d7b-9cf2-992878bf9e67" xlink:to="loc_us-gaap_MaturityUpTo30DaysMember_019fd749-6b74-70bc-8781-128b247ee2bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Maturity30To90DaysMember_019fd749-6b74-765d-a688-2be5acea8cc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Maturity30To90DaysMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019fd749-6b74-7d7b-9cf2-992878bf9e67" xlink:to="loc_us-gaap_Maturity30To90DaysMember_019fd749-6b74-765d-a688-2be5acea8cc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaturityOver90DaysMember_019fd749-6b74-73f9-8e78-fed47119a7a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MaturityOver90DaysMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_019fd749-6b74-7d7b-9cf2-992878bf9e67" xlink:to="loc_us-gaap_MaturityOver90DaysMember_019fd749-6b74-73f9-8e78-fed47119a7a5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis_019fd749-6b74-7647-ae0d-1a8ae1d178ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable_019fd749-6b74-781c-8128-a5ac2edf6150" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis_019fd749-6b74-7647-ae0d-1a8ae1d178ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019fd749-6b74-7647-ae0d-1a8ae1d178ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis_019fd749-6b74-7647-ae0d-1a8ae1d178ee" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019fd749-6b74-7647-ae0d-1a8ae1d178ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019fd749-6b74-7c8f-9904-4020fbf0f097" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis_019fd749-6b74-7647-ae0d-1a8ae1d178ee" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019fd749-6b74-7c8f-9904-4020fbf0f097" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019fd749-6b74-7738-9643-d6372be1404d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseTypeDomain_019fd749-6b74-7c8f-9904-4020fbf0f097" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019fd749-6b74-7738-9643-d6372be1404d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019fd749-6b74-7e61-8225-b2659e1eb0c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems_019fd749-6b74-7c70-84c9-acf7dfdfc085" xlink:to="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019fd749-6b74-7e61-8225-b2659e1eb0c4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/FEDERALHOMELOANBANKADVANCESScheduleofFHLBAdvancesDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#FEDERALHOMELOANBANKADVANCESScheduleofFHLBAdvancesDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/FEDERALHOMELOANBANKADVANCESScheduleofFHLBAdvancesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesLineItems_019fd749-6b74-70a9-95e5-c22d26c1b907" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankAdvancesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesTable_019fd749-6b74-717c-8f26-6d0af41d3b1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankAdvancesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesLineItems_019fd749-6b74-70a9-95e5-c22d26c1b907" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesTable_019fd749-6b74-717c-8f26-6d0af41d3b1a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd749-6b74-7eff-aeb1-d22d77ee5fa8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesTable_019fd749-6b74-717c-8f26-6d0af41d3b1a" xlink:to="loc_srt_RangeAxis_019fd749-6b74-7eff-aeb1-d22d77ee5fa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-7eff-aeb1-d22d77ee5fa8_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd749-6b74-7eff-aeb1-d22d77ee5fa8" xlink:to="loc_srt_RangeMember_019fd749-6b74-7eff-aeb1-d22d77ee5fa8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-7352-b951-776c214be326" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd749-6b74-7eff-aeb1-d22d77ee5fa8" xlink:to="loc_srt_RangeMember_019fd749-6b74-7352-b951-776c214be326" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd749-6b74-7612-8724-b910e95dae02" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-7352-b951-776c214be326" xlink:to="loc_srt_MinimumMember_019fd749-6b74-7612-8724-b910e95dae02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd749-6b74-7df9-9a7c-54f4ea11c9b8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-7352-b951-776c214be326" xlink:to="loc_srt_MaximumMember_019fd749-6b74-7df9-9a7c-54f4ea11c9b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-757d-a174-7ccb7f2bbb94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesTable_019fd749-6b74-717c-8f26-6d0af41d3b1a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-757d-a174-7ccb7f2bbb94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-757d-a174-7ccb7f2bbb94_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-757d-a174-7ccb7f2bbb94" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-757d-a174-7ccb7f2bbb94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7453-8446-d6e08174ba65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-757d-a174-7ccb7f2bbb94" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7453-8446-d6e08174ba65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesMember_019fd749-6b74-74ac-87a9-5743dc6bf82c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankAdvancesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7453-8446-d6e08174ba65" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesMember_019fd749-6b74-74ac-87a9-5743dc6bf82c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_019fd749-6b74-79f2-9141-8341ace2b728" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtPercentageBearingFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesLineItems_019fd749-6b74-70a9-95e5-c22d26c1b907" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_019fd749-6b74-79f2-9141-8341ace2b728" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019fd749-6b74-74a6-a8ae-e2e4dbe03531" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtPercentageBearingVariableInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesLineItems_019fd749-6b74-70a9-95e5-c22d26c1b907" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019fd749-6b74-74a6-a8ae-e2e4dbe03531" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesLongTerm_019fd749-6b74-76d7-8d55-576521faf502" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankAdvancesLongTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesLineItems_019fd749-6b74-70a9-95e5-c22d26c1b907" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesLongTerm_019fd749-6b74-76d7-8d55-576521faf502" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_AdvancesFromFederalHomeLoanBanksFairValueHedgeBasisAdjustmentsAndUnamortizedPrepaymentFees_019fd749-6b74-75ed-9f63-59f683a8cdc8" xlink:href="onb-20260930.xsd#onb_AdvancesFromFederalHomeLoanBanksFairValueHedgeBasisAdjustmentsAndUnamortizedPrepaymentFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesLineItems_019fd749-6b74-70a9-95e5-c22d26c1b907" xlink:to="loc_onb_AdvancesFromFederalHomeLoanBanksFairValueHedgeBasisAdjustmentsAndUnamortizedPrepaymentFees_019fd749-6b74-75ed-9f63-59f683a8cdc8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvancesFromFederalHomeLoanBanks_019fd749-6b74-7171-b7f9-70f273e9727f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdvancesFromFederalHomeLoanBanks"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesLineItems_019fd749-6b74-70a9-95e5-c22d26c1b907" xlink:to="loc_us-gaap_AdvancesFromFederalHomeLoanBanks_019fd749-6b74-7171-b7f9-70f273e9727f" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/OTHERBORROWINGSScheduleofOtherBorrowingsDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#OTHERBORROWINGSScheduleofOtherBorrowingsDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/OTHERBORROWINGSScheduleofOtherBorrowingsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7545-a3dc-5855c80e7fdd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7545-a3dc-5855c80e7fdd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019fd749-6b74-792a-9d6f-399ce3089a55" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7545-a3dc-5855c80e7fdd" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019fd749-6b74-792a-9d6f-399ce3089a55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-792a-9d6f-399ce3089a55_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019fd749-6b74-792a-9d6f-399ce3089a55" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-792a-9d6f-399ce3089a55_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-7ce0-b1c6-0c06f2f2eb96" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019fd749-6b74-792a-9d6f-399ce3089a55" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-7ce0-b1c6-0c06f2f2eb96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_019fd749-6b74-7e70-9fd3-cf03727c20cb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-7ce0-b1c6-0c06f2f2eb96" xlink:to="loc_srt_ParentCompanyMember_019fd749-6b74-7e70-9fd3-cf03727c20cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7966-a54c-5729d00e086b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7545-a3dc-5855c80e7fdd" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7966-a54c-5729d00e086b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7966-a54c-5729d00e086b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7966-a54c-5729d00e086b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7966-a54c-5729d00e086b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7198-973e-1d8e3b2b2bb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7966-a54c-5729d00e086b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7198-973e-1d8e3b2b2bb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_019fd749-6b74-7b94-adc9-51489e0192c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7198-973e-1d8e3b2b2bb5" xlink:to="loc_us-gaap_SubordinatedDebtMember_019fd749-6b74-7b94-adc9-51489e0192c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_JuniorSubordinatedDebtMember_019fd749-6b74-7e6c-a8e9-714c47ff2faf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_JuniorSubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7198-973e-1d8e3b2b2bb5" xlink:to="loc_us-gaap_JuniorSubordinatedDebtMember_019fd749-6b74-7e6c-a8e9-714c47ff2faf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableToBanksMember_019fd749-6b74-7dc3-b905-61b032e26646" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableToBanksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7198-973e-1d8e3b2b2bb5" xlink:to="loc_us-gaap_NotesPayableToBanksMember_019fd749-6b74-7dc3-b905-61b032e26646" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd749-6b74-73db-a343-98a4eafb02a0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7545-a3dc-5855c80e7fdd" xlink:to="loc_srt_RangeAxis_019fd749-6b74-73db-a343-98a4eafb02a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-73db-a343-98a4eafb02a0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd749-6b74-73db-a343-98a4eafb02a0" xlink:to="loc_srt_RangeMember_019fd749-6b74-73db-a343-98a4eafb02a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-7de3-a5ff-68bab3db6218" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd749-6b74-73db-a343-98a4eafb02a0" xlink:to="loc_srt_RangeMember_019fd749-6b74-7de3-a5ff-68bab3db6218" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd749-6b74-71b4-8cea-7a9cedd2c20d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-7de3-a5ff-68bab3db6218" xlink:to="loc_srt_MinimumMember_019fd749-6b74-71b4-8cea-7a9cedd2c20d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd749-6b74-70a8-a7e7-5d954cd7d897" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-7de3-a5ff-68bab3db6218" xlink:to="loc_srt_MaximumMember_019fd749-6b74-70a8-a7e7-5d954cd7d897" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019fd749-6b74-7a79-9ffb-c82250c037b9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7545-a3dc-5855c80e7fdd" xlink:to="loc_dei_LegalEntityAxis_019fd749-6b74-7a79-9ffb-c82250c037b9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019fd749-6b74-7a79-9ffb-c82250c037b9_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019fd749-6b74-7a79-9ffb-c82250c037b9" xlink:to="loc_dei_EntityDomain_019fd749-6b74-7a79-9ffb-c82250c037b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019fd749-6b74-7cf4-9569-d88be5f3d524" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019fd749-6b74-7a79-9ffb-c82250c037b9" xlink:to="loc_dei_EntityDomain_019fd749-6b74-7cf4-9569-d88be5f3d524" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OldNationalBankMember_019fd749-6b74-7dec-9a64-5abb1ada20b3" xlink:href="onb-20260930.xsd#onb_OldNationalBankMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019fd749-6b74-7cf4-9569-d88be5f3d524" xlink:to="loc_onb_OldNationalBankMember_019fd749-6b74-7dec-9a64-5abb1ada20b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_019fd749-6b74-7282-96a4-be63364c0d33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtPercentageBearingFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_019fd749-6b74-7282-96a4-be63364c0d33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebt_019fd749-6b74-769d-85bb-223a794368d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubordinatedDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_SubordinatedDebt_019fd749-6b74-769d-85bb-223a794368d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_019fd749-6b74-7a8c-b3e3-3d74d27dc219" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_019fd749-6b74-7a8c-b3e3-3d74d27dc219" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019fd749-6b74-7c5d-85b3-60eb815644d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtPercentageBearingVariableInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019fd749-6b74-7c5d-85b3-60eb815644d2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_JuniorSubordinatedNotes_019fd749-6b74-78d7-8832-20152010f05b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_JuniorSubordinatedNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_JuniorSubordinatedNotes_019fd749-6b74-78d7-8832-20152010f05b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherBasisAdjustments_019fd749-6b74-7c54-bf68-fe4d5c560acc" xlink:href="onb-20260930.xsd#onb_OtherBasisAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_onb_OtherBasisAdjustments_019fd749-6b74-7c54-bf68-fe4d5c560acc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiability_019fd749-6b74-7504-87bc-4a30c959ce84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinanceLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_FinanceLeaseLiability_019fd749-6b74-7504-87bc-4a30c959ce84" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableToBank_019fd749-6b74-719a-b167-62a53b6bcfb5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NotesPayableToBank"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_NotesPayableToBank_019fd749-6b74-719a-b167-62a53b6bcfb5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherBorrowings_019fd749-6b74-766f-a450-53e54942f245" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_us-gaap_OtherBorrowings_019fd749-6b74-766f-a450-53e54942f245" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_DerivativeInstrumentsCollateralizedPositionAmount_019fd749-6b74-77b7-8452-6fcca9ab29bf" xlink:href="onb-20260930.xsd#onb_DerivativeInstrumentsCollateralizedPositionAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-79de-8252-3a7502e967d5" xlink:to="loc_onb_DerivativeInstrumentsCollateralizedPositionAmount_019fd749-6b74-77b7-8452-6fcca9ab29bf" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/OTHERBORROWINGSAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#OTHERBORROWINGSAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/OTHERBORROWINGSAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7b48-8ecb-5ac63b19cf5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:to="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7b48-8ecb-5ac63b19cf5c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd749-6b74-7118-94c3-f98364d376bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7b48-8ecb-5ac63b19cf5c" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd749-6b74-7118-94c3-f98364d376bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-7118-94c3-f98364d376bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd749-6b74-7118-94c3-f98364d376bd" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-7118-94c3-f98364d376bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-71d6-9fb5-b5db1c0ad8d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd749-6b74-7118-94c3-f98364d376bd" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-71d6-9fb5-b5db1c0ad8d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_SubordinatedNotesMaturingJanuary2026Member_019fd749-6b74-7b97-b7e8-9c2499bfd0e0" xlink:href="onb-20260930.xsd#onb_SubordinatedNotesMaturingJanuary2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-71d6-9fb5-b5db1c0ad8d5" xlink:to="loc_onb_SubordinatedNotesMaturingJanuary2026Member_019fd749-6b74-7b97-b7e8-9c2499bfd0e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7b99-9364-aeb9d0b20999" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7b48-8ecb-5ac63b19cf5c" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7b99-9364-aeb9d0b20999" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7b99-9364-aeb9d0b20999_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7b99-9364-aeb9d0b20999" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7b99-9364-aeb9d0b20999_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-73ca-8f98-0097760cbb5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7b99-9364-aeb9d0b20999" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-73ca-8f98-0097760cbb5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_019fd749-6b74-7c0b-b994-8afc8d3e3ef3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-73ca-8f98-0097760cbb5a" xlink:to="loc_us-gaap_SubordinatedDebtMember_019fd749-6b74-7c0b-b994-8afc8d3e3ef3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6b74-737d-86b6-23a977bf76ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7b48-8ecb-5ac63b19cf5c" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6b74-737d-86b6-23a977bf76ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-737d-86b6-23a977bf76ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6b74-737d-86b6-23a977bf76ad" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-737d-86b6-23a977bf76ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-73d5-bb9f-19b9f1f78b05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6b74-737d-86b6-23a977bf76ad" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-73d5-bb9f-19b9f1f78b05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FirstMidwestBancorpIncMember_019fd749-6b74-7d1c-ba25-dcbec8f36506" xlink:href="onb-20260930.xsd#onb_FirstMidwestBancorpIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-73d5-bb9f-19b9f1f78b05" xlink:to="loc_onb_FirstMidwestBancorpIncMember_019fd749-6b74-7d1c-ba25-dcbec8f36506" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019fd749-6b74-78ef-8343-bada6942ca62" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-7b48-8ecb-5ac63b19cf5c" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019fd749-6b74-78ef-8343-bada6942ca62" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-78ef-8343-bada6942ca62_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019fd749-6b74-78ef-8343-bada6942ca62" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-78ef-8343-bada6942ca62_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-7c6d-8b8c-7158756d31fe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019fd749-6b74-78ef-8343-bada6942ca62" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-7c6d-8b8c-7158756d31fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_019fd749-6b74-7c00-bd78-c1092bf18958" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019fd749-6b74-7c6d-8b8c-7158756d31fe" xlink:to="loc_srt_ParentCompanyMember_019fd749-6b74-7c00-bd78-c1092bf18958" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd749-6b74-73f8-80e5-f349eae65d38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd749-6b74-73f8-80e5-f349eae65d38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd749-6b74-718b-ba89-63ae94b7330a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fd749-6b74-718b-ba89-63ae94b7330a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fd749-6b74-71cd-aca7-74a14eb90993" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fd749-6b74-71cd-aca7-74a14eb90993" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt_019fd749-6b74-76ac-9323-d8f1400390b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt_019fd749-6b74-76ac-9323-d8f1400390b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_019fd749-6b74-7b9d-8274-a2e434809f65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtPercentageBearingFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_019fd749-6b74-7b9d-8274-a2e434809f65" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LeveragedLoansCompliancePeriod_019fd749-6b74-7103-9c97-0db6c5e27d22" xlink:href="onb-20260930.xsd#onb_LeveragedLoansCompliancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:to="loc_onb_LeveragedLoansCompliancePeriod_019fd749-6b74-7103-9c97-0db6c5e27d22" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiability_019fd749-6b74-7d73-9cbf-3ecd99c662e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinanceLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7d01-bbd0-1257e8abdb9d" xlink:to="loc_us-gaap_FinanceLeaseLiability_019fd749-6b74-7d73-9cbf-3ecd99c662e1" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/OTHERBORROWINGSScheduleofTermsofOutstandingJuniorSubordinatedDebenturesDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#OTHERBORROWINGSScheduleofTermsofOutstandingJuniorSubordinatedDebenturesDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/OTHERBORROWINGSScheduleofTermsofOutstandingJuniorSubordinatedDebenturesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7327-9b90-c4b84d1690a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-74d5-ba4a-76ea0816e52b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7327-9b90-c4b84d1690a6" xlink:to="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-74d5-ba4a-76ea0816e52b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fd749-6b74-709b-b056-c61b70105c20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-74d5-ba4a-76ea0816e52b" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fd749-6b74-709b-b056-c61b70105c20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-709b-b056-c61b70105c20_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd749-6b74-709b-b056-c61b70105c20" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-709b-b056-c61b70105c20_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-7d7f-8d1e-c4abef407c8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019fd749-6b74-709b-b056-c61b70105c20" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-7d7f-8d1e-c4abef407c8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_TrustPreferredSecuritiesMember_019fd749-6b74-78a8-a2d1-87ea5fd3ed69" xlink:href="onb-20260930.xsd#onb_TrustPreferredSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fd749-6b74-7d7f-8d1e-c4abef407c8e" xlink:to="loc_onb_TrustPreferredSecuritiesMember_019fd749-6b74-78a8-a2d1-87ea5fd3ed69" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7224-8f84-4eb0e87837ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-74d5-ba4a-76ea0816e52b" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7224-8f84-4eb0e87837ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7224-8f84-4eb0e87837ca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7224-8f84-4eb0e87837ca" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-7224-8f84-4eb0e87837ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-778d-ad54-8ead505072f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019fd749-6b74-7224-8f84-4eb0e87837ca" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-778d-ad54-8ead505072f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_JuniorSubordinatedDebtMember_019fd749-6b74-762d-a40c-b7cf70921958" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_JuniorSubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fd749-6b74-778d-ad54-8ead505072f8" xlink:to="loc_us-gaap_JuniorSubordinatedDebtMember_019fd749-6b74-762d-a40c-b7cf70921958" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6b74-722e-b62c-ee17b435c7d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019fd749-6b74-74d5-ba4a-76ea0816e52b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6b74-722e-b62c-ee17b435c7d1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-722e-b62c-ee17b435c7d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6b74-722e-b62c-ee17b435c7d1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-722e-b62c-ee17b435c7d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd749-6b74-722e-b62c-ee17b435c7d1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BridgeviewStatutoryTrustIMember_019fd749-6b74-7439-86fa-d46858a43a99" xlink:href="onb-20260930.xsd#onb_BridgeviewStatutoryTrustIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_BridgeviewStatutoryTrustIMember_019fd749-6b74-7439-86fa-d46858a43a99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BridgeviewCapitalTrustIIMember_019fd749-6b74-78bc-8240-000491ff42ff" xlink:href="onb-20260930.xsd#onb_BridgeviewCapitalTrustIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_BridgeviewCapitalTrustIIMember_019fd749-6b74-78bc-8240-000491ff42ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FirstMidwestCapitalTrustIMember_019fd749-6b74-7231-a5ec-9c265ae037bc" xlink:href="onb-20260930.xsd#onb_FirstMidwestCapitalTrustIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_FirstMidwestCapitalTrustIMember_019fd749-6b74-7231-a5ec-9c265ae037bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_StJosephCapitalTrustIIMember_019fd749-6b74-72e0-870b-433d0a4f5354" xlink:href="onb-20260930.xsd#onb_StJosephCapitalTrustIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_StJosephCapitalTrustIIMember_019fd749-6b74-72e0-870b-433d0a4f5354" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_NorthernStatesStatutoryTrustIMember_019fd749-6b74-757d-ad5f-f282cc131ef9" xlink:href="onb-20260930.xsd#onb_NorthernStatesStatutoryTrustIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_NorthernStatesStatutoryTrustIMember_019fd749-6b74-757d-ad5f-f282cc131ef9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_AnchorCapitalTrustIIIMember_019fd749-6b74-7a91-9cfc-09b17219f497" xlink:href="onb-20260930.xsd#onb_AnchorCapitalTrustIIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_AnchorCapitalTrustIIIMember_019fd749-6b74-7a91-9cfc-09b17219f497" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_GreatLakesStatutoryTrustIIMember_019fd749-6b74-7637-b7d2-80abc3a6d0c1" xlink:href="onb-20260930.xsd#onb_GreatLakesStatutoryTrustIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_GreatLakesStatutoryTrustIIMember_019fd749-6b74-7637-b7d2-80abc3a6d0c1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_BremerStatutoryTrustIIMember_019fd749-6b74-79ca-9cb2-74e42112023f" xlink:href="onb-20260930.xsd#onb_BremerStatutoryTrustIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_BremerStatutoryTrustIIMember_019fd749-6b74-79ca-9cb2-74e42112023f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_HomeFederalStatutoryTrustIMember_019fd749-6b74-74bb-95de-fa17c606d258" xlink:href="onb-20260930.xsd#onb_HomeFederalStatutoryTrustIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_HomeFederalStatutoryTrustIMember_019fd749-6b74-74bb-95de-fa17c606d258" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_MonroeBancorpCapitalTrustIMember_019fd749-6b74-760e-9c46-f8d3649151b2" xlink:href="onb-20260930.xsd#onb_MonroeBancorpCapitalTrustIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_MonroeBancorpCapitalTrustIMember_019fd749-6b74-760e-9c46-f8d3649151b2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_TowerCapitalTrustThreeMember_019fd749-6b74-72b3-a002-8a280895ab71" xlink:href="onb-20260930.xsd#onb_TowerCapitalTrustThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_TowerCapitalTrustThreeMember_019fd749-6b74-72b3-a002-8a280895ab71" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_MonroeBancorpStatutoryTrustIIMember_019fd749-6b74-73f4-9748-1fbf4421265d" xlink:href="onb-20260930.xsd#onb_MonroeBancorpStatutoryTrustIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_MonroeBancorpStatutoryTrustIIMember_019fd749-6b74-73f4-9748-1fbf4421265d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_GreatLakesStatutoryTrustIIIMember_019fd749-6b74-7c16-ac8d-637cf9b0828b" xlink:href="onb-20260930.xsd#onb_GreatLakesStatutoryTrustIIIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd749-6b74-735e-9403-402501cd7fae" xlink:to="loc_onb_GreatLakesStatutoryTrustIIIMember_019fd749-6b74-7c16-ac8d-637cf9b0828b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019fd749-6b74-775a-a9fc-384a8e56b701" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7327-9b90-c4b84d1690a6" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019fd749-6b74-775a-a9fc-384a8e56b701" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fd749-6b74-7b94-b1f7-1947c321d5f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7327-9b90-c4b84d1690a6" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fd749-6b74-7b94-b1f7-1947c321d5f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_019fd749-6b74-7844-afd1-3b0abddd1bf7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtPercentageBearingFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7327-9b90-c4b84d1690a6" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingFixedInterestRate_019fd749-6b74-7844-afd1-3b0abddd1bf7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019fd749-6b74-7ecf-aa22-c740172b1634" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fd749-6b74-7327-9b90-c4b84d1690a6" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_019fd749-6b74-7ecf-aa22-c740172b1634" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSScheduleofAOCIDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSScheduleofAOCIDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSScheduleofAOCIDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fd749-6b74-7322-9314-4c8af2c591c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019fd749-6b74-7933-b397-82deaf5d7ea7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fd749-6b74-7322-9314-4c8af2c591c5" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019fd749-6b74-7933-b397-82deaf5d7ea7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6b74-79e2-b3d3-a19785f02728" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019fd749-6b74-7933-b397-82deaf5d7ea7" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6b74-79e2-b3d3-a19785f02728" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd749-6b74-79e2-b3d3-a19785f02728_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6b74-79e2-b3d3-a19785f02728" xlink:to="loc_us-gaap_EquityComponentDomain_019fd749-6b74-79e2-b3d3-a19785f02728_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7fac-9b2a-150b11c443ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6b74-79e2-b3d3-a19785f02728" xlink:to="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7fac-9b2a-150b11c443ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd749-6b74-7d19-a130-3edbffa9e8a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7fac-9b2a-150b11c443ef" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd749-6b74-7d19-a130-3edbffa9e8a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019fd749-6b74-70b4-b119-b5f9ba020542" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd749-6b74-7d19-a130-3edbffa9e8a1" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019fd749-6b74-70b4-b119-b5f9ba020542" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_AccumulatedUnrealizedGainsLossesOnHeldToMaturitySecuritiesParentMember_019fd749-6b74-7394-8739-854e6cb2d851" xlink:href="onb-20260930.xsd#onb_AccumulatedUnrealizedGainsLossesOnHeldToMaturitySecuritiesParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd749-6b74-7d19-a130-3edbffa9e8a1" xlink:to="loc_onb_AccumulatedUnrealizedGainsLossesOnHeldToMaturitySecuritiesParentMember_019fd749-6b74-7394-8739-854e6cb2d851" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019fd749-6b74-7e22-b419-3daa99ee8add" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fd749-6b74-7d19-a130-3edbffa9e8a1" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019fd749-6b74-7e22-b419-3daa99ee8add" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fd749-6b74-7c75-aa33-fb2233fe9ced" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fd749-6b74-7322-9314-4c8af2c591c5" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fd749-6b74-7c75-aa33-fb2233fe9ced" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fd749-6b74-70c1-a992-70ddcb8fca04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fd749-6b74-7c75-aa33-fb2233fe9ced" xlink:to="loc_us-gaap_StockholdersEquity_019fd749-6b74-70c1-a992-70ddcb8fca04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent_019fd749-6b74-7f8d-b7df-749893c4719a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fd749-6b74-7c75-aa33-fb2233fe9ced" xlink:to="loc_us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent_019fd749-6b74-7f8d-b7df-749893c4719a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_019fd749-6b74-718b-bad0-7b06299366b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fd749-6b74-7c75-aa33-fb2233fe9ced" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_019fd749-6b74-718b-bad0-7b06299366b1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019fd749-6b74-74f0-b6f2-103cb8c92db5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSScheduleofReclassificationsoutofAOCIDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSScheduleofReclassificationsoutofAOCIDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSScheduleofReclassificationsoutofAOCIDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019fd749-6b74-7c67-accd-d37a5a92891f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019fd749-6b74-7831-96c8-8c5406a70e11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019fd749-6b74-7c67-accd-d37a5a92891f" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019fd749-6b74-7831-96c8-8c5406a70e11" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019fd749-6b74-73a5-a20f-42875b9d1309" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019fd749-6b74-7831-96c8-8c5406a70e11" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019fd749-6b74-73a5-a20f-42875b9d1309" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019fd749-6b74-73a5-a20f-42875b9d1309_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019fd749-6b74-73a5-a20f-42875b9d1309" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019fd749-6b74-73a5-a20f-42875b9d1309_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019fd749-6b74-7ae3-a170-60c90737a5ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019fd749-6b74-73a5-a20f-42875b9d1309" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019fd749-6b74-7ae3-a170-60c90737a5ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019fd749-6b74-719f-9d67-4020e0d1b4fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019fd749-6b74-7ae3-a170-60c90737a5ac" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019fd749-6b74-719f-9d67-4020e0d1b4fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6b74-7860-b2b3-d5fa62eecb95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019fd749-6b74-7831-96c8-8c5406a70e11" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6b74-7860-b2b3-d5fa62eecb95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7860-b2b3-d5fa62eecb95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6b74-7860-b2b3-d5fa62eecb95" xlink:to="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7860-b2b3-d5fa62eecb95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7b28-bbc2-351e68371df6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019fd749-6b74-7860-b2b3-d5fa62eecb95" xlink:to="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7b28-bbc2-351e68371df6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019fd749-6b74-7401-81b5-c8740f589fe9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7b28-bbc2-351e68371df6" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019fd749-6b74-7401-81b5-c8740f589fe9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_AccumulatedUnrealizedGainsLossesOnHeldToMaturitySecuritiesParentMember_019fd749-6b74-7484-9eb1-1799370a7274" xlink:href="onb-20260930.xsd#onb_AccumulatedUnrealizedGainsLossesOnHeldToMaturitySecuritiesParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7b28-bbc2-351e68371df6" xlink:to="loc_onb_AccumulatedUnrealizedGainsLossesOnHeldToMaturitySecuritiesParentMember_019fd749-6b74-7484-9eb1-1799370a7274" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019fd749-6b74-7846-899b-0c31d7a6b6fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fd749-6b74-7b28-bbc2-351e68371df6" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019fd749-6b74-7846-899b-0c31d7a6b6fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesGainLoss_019fd749-6b74-7a62-80e5-aa96189ec482" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtAndEquitySecuritiesGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019fd749-6b74-7c67-accd-d37a5a92891f" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesGainLoss_019fd749-6b74-7a62-80e5-aa96189ec482" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_019fd749-6b74-743f-ba48-f437340e1ce5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019fd749-6b74-7c67-accd-d37a5a92891f" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_019fd749-6b74-743f-ba48-f437340e1ce5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019fd749-6b74-7558-9f92-6766ee89ee8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019fd749-6b74-7c67-accd-d37a5a92891f" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019fd749-6b74-7558-9f92-6766ee89ee8a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fd749-6b74-7899-b99a-480c3a017b6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019fd749-6b74-7c67-accd-d37a5a92891f" xlink:to="loc_us-gaap_NetIncomeLoss_019fd749-6b74-7899-b99a-480c3a017b6d" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/INCOMETAXESAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#INCOMETAXESAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/INCOMETAXESAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_onb_IncomeTaxesLineItems_019fd749-6b74-7455-957a-f5e83a4732dc" xlink:href="onb-20260930.xsd#onb_IncomeTaxesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_IncomeTaxesTable_019fd749-6b74-7ae0-a25f-2a5afdcba154" xlink:href="onb-20260930.xsd#onb_IncomeTaxesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_onb_IncomeTaxesLineItems_019fd749-6b74-7455-957a-f5e83a4732dc" xlink:to="loc_onb_IncomeTaxesTable_019fd749-6b74-7ae0-a25f-2a5afdcba154" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019fd749-6b74-7a85-a6cf-83601c33a9df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_onb_IncomeTaxesTable_019fd749-6b74-7ae0-a25f-2a5afdcba154" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019fd749-6b74-7a85-a6cf-83601c33a9df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019fd749-6b74-7a85-a6cf-83601c33a9df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019fd749-6b74-7a85-a6cf-83601c33a9df" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019fd749-6b74-7a85-a6cf-83601c33a9df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019fd749-6b74-76a8-9265-92e1f0101ae9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019fd749-6b74-7a85-a6cf-83601c33a9df" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019fd749-6b74-76a8-9265-92e1f0101ae9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019fd749-6b74-7a28-b303-9a760d630280" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019fd749-6b74-76a8-9265-92e1f0101ae9" xlink:to="loc_us-gaap_DomesticCountryMember_019fd749-6b74-7a28-b303-9a760d630280" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019fd749-6b74-7b63-8ad6-175ffdb769ef" xlink:href="https://xbrl.sec.gov/country/2026/country-2026.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticCountryMember_019fd749-6b74-7a28-b303-9a760d630280" xlink:to="loc_country_US_019fd749-6b74-7b63-8ad6-175ffdb769ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_019fd749-6b74-7540-acc0-054885798fca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019fd749-6b74-76a8-9265-92e1f0101ae9" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_019fd749-6b74-7540-acc0-054885798fca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsLiabilitiesNet_019fd749-6b74-7f25-bb8d-2eed5b4982e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_onb_IncomeTaxesLineItems_019fd749-6b74-7455-957a-f5e83a4732dc" xlink:to="loc_us-gaap_DeferredTaxAssetsLiabilitiesNet_019fd749-6b74-7f25-bb8d-2eed5b4982e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_019fd749-6b74-756d-9c03-9cc89c933383" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_onb_IncomeTaxesLineItems_019fd749-6b74-7455-957a-f5e83a4732dc" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_019fd749-6b74-756d-9c03-9cc89c933383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_019fd749-6b74-7d65-af02-7677e7f77cbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_onb_IncomeTaxesLineItems_019fd749-6b74-7455-957a-f5e83a4732dc" xlink:to="loc_us-gaap_OperatingLossCarryforwards_019fd749-6b74-7d65-af02-7677e7f77cbc" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/DERIVATIVEFINANCIALINSTRUMENTSAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/DERIVATIVEFINANCIALINSTRUMENTSAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7158-bd1e-49a14d5bbc19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019fd749-6b74-7024-a020-d362d55b1161" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7158-bd1e-49a14d5bbc19" xlink:to="loc_us-gaap_DerivativeTable_019fd749-6b74-7024-a020-d362d55b1161" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-725f-8036-44c8b4119cfe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd749-6b74-7024-a020-d362d55b1161" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-725f-8036-44c8b4119cfe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-725f-8036-44c8b4119cfe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-725f-8036-44c8b4119cfe" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-725f-8036-44c8b4119cfe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7967-a3e2-ae2cd5107e20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-725f-8036-44c8b4119cfe" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7967-a3e2-ae2cd5107e20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_VariableInterestRateSwapBorrowingsMember_019fd749-6b74-720f-8e2e-b79c5abbff76" xlink:href="onb-20260930.xsd#onb_VariableInterestRateSwapBorrowingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7967-a3e2-ae2cd5107e20" xlink:to="loc_onb_VariableInterestRateSwapBorrowingsMember_019fd749-6b74-720f-8e2e-b79c5abbff76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_VariableInterestRateSwapsCollarsAndFloorsMember_019fd749-6b74-7c73-aaca-a475af45bd26" xlink:href="onb-20260930.xsd#onb_VariableInterestRateSwapsCollarsAndFloorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7967-a3e2-ae2cd5107e20" xlink:to="loc_onb_VariableInterestRateSwapsCollarsAndFloorsMember_019fd749-6b74-7c73-aaca-a475af45bd26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember_019fd749-6b74-726a-9a45-627b48f757f3" xlink:href="onb-20260930.xsd#onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7967-a3e2-ae2cd5107e20" xlink:to="loc_onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember_019fd749-6b74-726a-9a45-627b48f757f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateLockCommitmentsMember_019fd749-6b74-7fee-9bab-e70c64b262bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateLockCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7967-a3e2-ae2cd5107e20" xlink:to="loc_us-gaap_InterestRateLockCommitmentsMember_019fd749-6b74-7fee-9bab-e70c64b262bf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ForwardCommitmentsMember_019fd749-6b74-7bce-8a35-dfee31536a5b" xlink:href="onb-20260930.xsd#onb_ForwardCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7967-a3e2-ae2cd5107e20" xlink:to="loc_onb_ForwardCommitmentsMember_019fd749-6b74-7bce-8a35-dfee31536a5b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CustomerAndOffsettingCounterpartyDerivativeInstrumentsMember_019fd749-6b74-77fc-95ee-362a05f99fb0" xlink:href="onb-20260930.xsd#onb_CustomerAndOffsettingCounterpartyDerivativeInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7967-a3e2-ae2cd5107e20" xlink:to="loc_onb_CustomerAndOffsettingCounterpartyDerivativeInstrumentsMember_019fd749-6b74-77fc-95ee-362a05f99fb0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-7ff9-90b9-053ad54994d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd749-6b74-7024-a020-d362d55b1161" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-7ff9-90b9-053ad54994d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-7ff9-90b9-053ad54994d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-7ff9-90b9-053ad54994d8" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-7ff9-90b9-053ad54994d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-79be-a079-d8ba9e371c9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-7ff9-90b9-053ad54994d8" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-79be-a079-d8ba9e371c9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019fd749-6b74-7cff-9795-0a62cae9f01b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-79be-a079-d8ba9e371c9e" xlink:to="loc_us-gaap_CashFlowHedgingMember_019fd749-6b74-7cff-9795-0a62cae9f01b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019fd749-6b74-71e6-8468-46779440397b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-79be-a079-d8ba9e371c9e" xlink:to="loc_us-gaap_FairValueHedgingMember_019fd749-6b74-71e6-8468-46779440397b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-715b-8095-e57e7156ef43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd749-6b74-7024-a020-d362d55b1161" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-715b-8095-e57e7156ef43" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-715b-8095-e57e7156ef43_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-715b-8095-e57e7156ef43" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-715b-8095-e57e7156ef43_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7f2e-b85d-f84586d41a31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-715b-8095-e57e7156ef43" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7f2e-b85d-f84586d41a31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fd749-6b74-723b-9d64-0bb3e0d02f38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7f2e-b85d-f84586d41a31" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fd749-6b74-723b-9d64-0bb3e0d02f38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019fd749-6b74-7466-baf1-ff812c42c5d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7f2e-b85d-f84586d41a31" xlink:to="loc_us-gaap_NondesignatedMember_019fd749-6b74-7466-baf1-ff812c42c5d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_PercentageOfPeriodicChangesInFairValueQualifiesForHedgeAccounting_019fd749-6b74-77f4-b83a-91d92f53fd76" xlink:href="onb-20260930.xsd#onb_PercentageOfPeriodicChangesInFairValueQualifiesForHedgeAccounting"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7158-bd1e-49a14d5bbc19" xlink:to="loc_onb_PercentageOfPeriodicChangesInFairValueQualifiesForHedgeAccounting_019fd749-6b74-77f4-b83a-91d92f53fd76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019fd749-6b74-7b9e-bac3-1be9e6338c38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7158-bd1e-49a14d5bbc19" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019fd749-6b74-7b9e-bac3-1be9e6338c38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_InterestRateCashFlowHedgeGainLossToBeReclassifiedToInterestIncomeDuringNext12MonthsNet_019fd749-6b74-7f61-b4bf-e0d4c5379b94" xlink:href="onb-20260930.xsd#onb_InterestRateCashFlowHedgeGainLossToBeReclassifiedToInterestIncomeDuringNext12MonthsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7158-bd1e-49a14d5bbc19" xlink:to="loc_onb_InterestRateCashFlowHedgeGainLossToBeReclassifiedToInterestIncomeDuringNext12MonthsNet_019fd749-6b74-7f61-b4bf-e0d4c5379b94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_InterestRateCashFlowHedgeGainLossToBeReclassifiedToInterestExpenseDuringNext12MonthsNet_019fd749-6b74-7988-b896-6c7032ba0732" xlink:href="onb-20260930.xsd#onb_InterestRateCashFlowHedgeGainLossToBeReclassifiedToInterestExpenseDuringNext12MonthsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7158-bd1e-49a14d5bbc19" xlink:to="loc_onb_InterestRateCashFlowHedgeGainLossToBeReclassifiedToInterestExpenseDuringNext12MonthsNet_019fd749-6b74-7988-b896-6c7032ba0732" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/DERIVATIVEFINANCIALINSTRUMENTSScheduleofFairValueofDerivativeFinancialInstrumentsDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSScheduleofFairValueofDerivativeFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/DERIVATIVEFINANCIALINSTRUMENTSScheduleofFairValueofDerivativeFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7f36-b4a6-5eb5add20d80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019fd749-6b74-7afd-b433-788766bacd9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7f36-b4a6-5eb5add20d80" xlink:to="loc_us-gaap_DerivativeTable_019fd749-6b74-7afd-b433-788766bacd9b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-7d3c-911f-4d1ca132d3fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd749-6b74-7afd-b433-788766bacd9b" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-7d3c-911f-4d1ca132d3fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7d3c-911f-4d1ca132d3fd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-7d3c-911f-4d1ca132d3fd" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7d3c-911f-4d1ca132d3fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7230-9721-b4907faec2b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-7d3c-911f-4d1ca132d3fd" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7230-9721-b4907faec2b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fd749-6b74-7d1c-a115-eaa5a9652b12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7230-9721-b4907faec2b4" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fd749-6b74-7d1c-a115-eaa5a9652b12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019fd749-6b74-7a4a-9e28-6b03bf7488b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7230-9721-b4907faec2b4" xlink:to="loc_us-gaap_NondesignatedMember_019fd749-6b74-7a4a-9e28-6b03bf7488b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-74f8-88f3-7a4a2b4ed45c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd749-6b74-7afd-b433-788766bacd9b" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-74f8-88f3-7a4a2b4ed45c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-74f8-88f3-7a4a2b4ed45c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-74f8-88f3-7a4a2b4ed45c" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-74f8-88f3-7a4a2b4ed45c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-746a-81bf-dc2d5a88df97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-74f8-88f3-7a4a2b4ed45c" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-746a-81bf-dc2d5a88df97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019fd749-6b74-7e4b-b5bd-d78abec123f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-746a-81bf-dc2d5a88df97" xlink:to="loc_us-gaap_CashFlowHedgingMember_019fd749-6b74-7e4b-b5bd-d78abec123f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019fd749-6b74-7fd5-91bb-45429228b6aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-746a-81bf-dc2d5a88df97" xlink:to="loc_us-gaap_FairValueHedgingMember_019fd749-6b74-7fd5-91bb-45429228b6aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-7ec3-9844-f4208aaf1e49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019fd749-6b74-7afd-b433-788766bacd9b" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-7ec3-9844-f4208aaf1e49" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7ec3-9844-f4208aaf1e49_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-7ec3-9844-f4208aaf1e49" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7ec3-9844-f4208aaf1e49_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-7ec3-9844-f4208aaf1e49" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_VariableInterestRateSwapsCollarsAndFloorsMember_019fd749-6b74-7d63-b69a-13a2c42cfb60" xlink:href="onb-20260930.xsd#onb_VariableInterestRateSwapsCollarsAndFloorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_onb_VariableInterestRateSwapsCollarsAndFloorsMember_019fd749-6b74-7d63-b69a-13a2c42cfb60" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_VariableInterestRateSwapBorrowingsMember_019fd749-6b74-7a6c-9c7f-a4b5f04cfa37" xlink:href="onb-20260930.xsd#onb_VariableInterestRateSwapBorrowingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_onb_VariableInterestRateSwapBorrowingsMember_019fd749-6b74-7a6c-9c7f-a4b5f04cfa37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember_019fd749-6b74-7feb-b6ac-09040f017a71" xlink:href="onb-20260930.xsd#onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember_019fd749-6b74-7feb-b6ac-09040f017a71" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateLockCommitmentsMember_019fd749-6b74-71cf-9a80-1df2458657f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateLockCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_us-gaap_InterestRateLockCommitmentsMember_019fd749-6b74-71cf-9a80-1df2458657f3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ForwardCommitmentsMember_019fd749-6b74-770d-8241-2ab67dd82382" xlink:href="onb-20260930.xsd#onb_ForwardCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_onb_ForwardCommitmentsMember_019fd749-6b74-770d-8241-2ab67dd82382" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CustomerDerivativeInstrumentMember_019fd749-6b74-70c9-a963-7d4cdd20b035" xlink:href="onb-20260930.xsd#onb_CustomerDerivativeInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_onb_CustomerDerivativeInstrumentMember_019fd749-6b74-70c9-a963-7d4cdd20b035" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OffsettingCounterPartyDerivativeInstrumentMember_019fd749-6b74-793d-b3b6-d530230a83bc" xlink:href="onb-20260930.xsd#onb_OffsettingCounterPartyDerivativeInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_onb_OffsettingCounterPartyDerivativeInstrumentMember_019fd749-6b74-793d-b3b6-d530230a83bc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CustomerForeignExchangeForwardMember_019fd749-6b74-701c-be87-afd223d6123c" xlink:href="onb-20260930.xsd#onb_CustomerForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_onb_CustomerForeignExchangeForwardMember_019fd749-6b74-701c-be87-afd223d6123c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CounterpartyForeignExchangeForwardMember_019fd749-6b74-7cc5-9339-d2c5d55bfe56" xlink:href="onb-20260930.xsd#onb_CounterpartyForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-76de-9f07-86e129764422" xlink:to="loc_onb_CounterpartyForeignExchangeForwardMember_019fd749-6b74-7cc5-9339-d2c5d55bfe56" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019fd749-6b74-78c3-ba47-df4dae91044f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7f36-b4a6-5eb5add20d80" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019fd749-6b74-78c3-ba47-df4dae91044f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019fd749-6b74-7b33-97a2-4e6b63f21967" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7f36-b4a6-5eb5add20d80" xlink:to="loc_us-gaap_DerivativeAssets_019fd749-6b74-7b33-97a2-4e6b63f21967" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019fd749-6b74-7712-b041-62cbbb21a17c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019fd749-6b74-7f36-b4a6-5eb5add20d80" xlink:to="loc_us-gaap_DerivativeLiabilities_019fd749-6b74-7712-b041-62cbbb21a17c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/DERIVATIVEFINANCIALINSTRUMENTSScheduleofEffectofDerivativeInstrumentsontheConsolidatedStatementsofIncomeDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#DERIVATIVEFINANCIALINSTRUMENTSScheduleofEffectofDerivativeInstrumentsontheConsolidatedStatementsofIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/DERIVATIVEFINANCIALINSTRUMENTSScheduleofEffectofDerivativeInstrumentsontheConsolidatedStatementsofIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019fd749-6b74-7b42-bf07-4f2ccf9522c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019fd749-6b74-76ea-8ce8-721d87e06ae0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019fd749-6b74-7b42-bf07-4f2ccf9522c0" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019fd749-6b74-76ea-8ce8-721d87e06ae0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-73d2-80ac-4c2cbb67c3e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019fd749-6b74-76ea-8ce8-721d87e06ae0" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-73d2-80ac-4c2cbb67c3e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-73d2-80ac-4c2cbb67c3e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-73d2-80ac-4c2cbb67c3e2" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-73d2-80ac-4c2cbb67c3e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7382-8f4c-b0e981e3d1e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-73d2-80ac-4c2cbb67c3e2" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7382-8f4c-b0e981e3d1e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_VariableInterestRateSwapBorrowingsMember_019fd749-6b74-79d3-8214-def325b4ef8c" xlink:href="onb-20260930.xsd#onb_VariableInterestRateSwapBorrowingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7382-8f4c-b0e981e3d1e2" xlink:to="loc_onb_VariableInterestRateSwapBorrowingsMember_019fd749-6b74-79d3-8214-def325b4ef8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember_019fd749-6b74-7d5d-8f70-1b9c83049534" xlink:href="onb-20260930.xsd#onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7382-8f4c-b0e981e3d1e2" xlink:to="loc_onb_VariableInterestRateSwapAvailableForSaleInvestmentSecuritiesMember_019fd749-6b74-7d5d-8f70-1b9c83049534" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019fd749-6b74-7f42-aeb0-28df3de44358" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7382-8f4c-b0e981e3d1e2" xlink:to="loc_us-gaap_InterestRateContractMember_019fd749-6b74-7f42-aeb0-28df3de44358" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_MortgageContractMember_019fd749-6b74-7858-8d06-ff9e1346f507" xlink:href="onb-20260930.xsd#onb_MortgageContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7382-8f4c-b0e981e3d1e2" xlink:to="loc_onb_MortgageContractMember_019fd749-6b74-7858-8d06-ff9e1346f507" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_019fd749-6b74-7981-9c25-cb869144e4da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7382-8f4c-b0e981e3d1e2" xlink:to="loc_us-gaap_ForeignExchangeContractMember_019fd749-6b74-7981-9c25-cb869144e4da" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-7e3a-bb0e-fe90647971f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019fd749-6b74-76ea-8ce8-721d87e06ae0" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-7e3a-bb0e-fe90647971f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-7e3a-bb0e-fe90647971f3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-7e3a-bb0e-fe90647971f3" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-7e3a-bb0e-fe90647971f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-7562-8ff8-f31d2ab76285" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fd749-6b74-7e3a-bb0e-fe90647971f3" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-7562-8ff8-f31d2ab76285" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019fd749-6b74-7f51-9115-edb1f533f3fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019fd749-6b74-7562-8ff8-f31d2ab76285" xlink:to="loc_us-gaap_FairValueHedgingMember_019fd749-6b74-7f51-9115-edb1f533f3fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-7959-a079-e3ad16a13c92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019fd749-6b74-76ea-8ce8-721d87e06ae0" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-7959-a079-e3ad16a13c92" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7959-a079-e3ad16a13c92_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-7959-a079-e3ad16a13c92" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7959-a079-e3ad16a13c92_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7d82-af2d-6966d492e6b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019fd749-6b74-7959-a079-e3ad16a13c92" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7d82-af2d-6966d492e6b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019fd749-6b74-7799-a34e-0ebb808f9111" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019fd749-6b74-7d82-af2d-6966d492e6b6" xlink:to="loc_us-gaap_NondesignatedMember_019fd749-6b74-7799-a34e-0ebb808f9111" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019fd749-6b74-7231-8e0b-9dc21b13d570" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019fd749-6b74-7b42-bf07-4f2ccf9522c0" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019fd749-6b74-7231-8e0b-9dc21b13d570" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings_019fd749-6b74-76bb-a68d-2be0c46e965e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019fd749-6b74-7b42-bf07-4f2ccf9522c0" xlink:to="loc_us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings_019fd749-6b74-76bb-a68d-2be0c46e965e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019fd749-6b74-7e7b-a54f-b6a883f1edea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019fd749-6b74-7b42-bf07-4f2ccf9522c0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019fd749-6b74-7e7b-a54f-b6a883f1edea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019fd749-6b74-7cd7-8218-02e83ac83047" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019fd749-6b74-7b42-bf07-4f2ccf9522c0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019fd749-6b74-7cd7-8218-02e83ac83047" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/COMMITMENTSCONTINGENCIESANDFINANCIALGUARANTEESAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#COMMITMENTSCONTINGENCIESANDFINANCIALGUARANTEESAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/COMMITMENTSCONTINGENCIESANDFINANCIALGUARANTEESAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019fd749-6b74-72a7-bec2-7bb23bbff14c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019fd749-6b74-7c78-84a5-f65dc453eb0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fd749-6b74-72a7-bec2-7bb23bbff14c" xlink:to="loc_us-gaap_LossContingenciesTable_019fd749-6b74-7c78-84a5-f65dc453eb0d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-7053-af15-fb7436edfc3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019fd749-6b74-7c78-84a5-f65dc453eb0d" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-7053-af15-fb7436edfc3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7053-af15-fb7436edfc3a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-7053-af15-fb7436edfc3a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7053-af15-fb7436edfc3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7191-85d7-9d5bdcc3922c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019fd749-6b74-7053-af15-fb7436edfc3a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7191-85d7-9d5bdcc3922c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fd749-6b74-7a8c-997e-16334a7c928c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fd749-6b74-7191-85d7-9d5bdcc3922c" xlink:to="loc_us-gaap_InterestRateSwapMember_019fd749-6b74-7a8c-997e-16334a7c928c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_TermOfStandbyLettersOfCredit_019fd749-6b74-719d-a36d-c923777037ab" xlink:href="onb-20260930.xsd#onb_TermOfStandbyLettersOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fd749-6b74-72a7-bec2-7bb23bbff14c" xlink:to="loc_onb_TermOfStandbyLettersOfCredit_019fd749-6b74-719d-a36d-c923777037ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_PercentOfUnfundedLoanCommitmentsWithFixedRates_019fd749-6b74-7b2a-bd9b-2c276fde8397" xlink:href="onb-20260930.xsd#onb_PercentOfUnfundedLoanCommitmentsWithFixedRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fd749-6b74-72a7-bec2-7bb23bbff14c" xlink:to="loc_onb_PercentOfUnfundedLoanCommitmentsWithFixedRates_019fd749-6b74-7b2a-bd9b-2c276fde8397" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LoanCommitmentsFloatingInterestRateMinimum_019fd749-6b74-731e-92c1-be0e49be98a2" xlink:href="onb-20260930.xsd#onb_LoanCommitmentsFloatingInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fd749-6b74-72a7-bec2-7bb23bbff14c" xlink:to="loc_onb_LoanCommitmentsFloatingInterestRateMinimum_019fd749-6b74-731e-92c1-be0e49be98a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LoanCommitmentsFloatingInterestRateMaximum_019fd749-6b74-749f-a4a9-0ac582826db3" xlink:href="onb-20260930.xsd#onb_LoanCommitmentsFloatingInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fd749-6b74-72a7-bec2-7bb23bbff14c" xlink:to="loc_onb_LoanCommitmentsFloatingInterestRateMaximum_019fd749-6b74-749f-a4a9-0ac582826db3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_AllowanceForUnfundedLoanCommitments_019fd749-6b74-79e2-ab18-d3f3e96d2fae" xlink:href="onb-20260930.xsd#onb_AllowanceForUnfundedLoanCommitments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fd749-6b74-72a7-bec2-7bb23bbff14c" xlink:to="loc_onb_AllowanceForUnfundedLoanCommitments_019fd749-6b74-79e2-ab18-d3f3e96d2fae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019fd749-6b74-71c9-aaa7-c5f74533108b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019fd749-6b74-72a7-bec2-7bb23bbff14c" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019fd749-6b74-71c9-aaa7-c5f74533108b" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/FAIRVALUEScheduleofFairValueAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#FAIRVALUEScheduleofFairValueAssetsandLiabilitiesMeasuredonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/FAIRVALUEScheduleofFairValueAssetsandLiabilitiesMeasuredonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ddc-bee9-1f49c10d8330" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-7e04-b8e4-d64e183027cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ddc-bee9-1f49c10d8330" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-7e04-b8e4-d64e183027cc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b74-7453-b7f2-7d980b62d4c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-7e04-b8e4-d64e183027cc" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b74-7453-b7f2-7d980b62d4c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-7453-b7f2-7d980b62d4c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b74-7453-b7f2-7d980b62d4c8" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-7453-b7f2-7d980b62d4c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b74-712c-bf4b-350c84af4295" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b74-7453-b7f2-7d980b62d4c8" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b74-712c-bf4b-350c84af4295" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-72c7-8fb2-e4061ac5fd12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b74-712c-bf4b-350c84af4295" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-72c7-8fb2-e4061ac5fd12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019fd749-6b74-7113-b4d5-4d7fb611fa23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-72c7-8fb2-e4061ac5fd12" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019fd749-6b74-7113-b4d5-4d7fb611fa23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019fd749-6b74-72a0-abc9-6cc2a757f025" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-72c7-8fb2-e4061ac5fd12" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019fd749-6b74-72a0-abc9-6cc2a757f025" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019fd749-6b74-7f80-a1c5-e53bf79c67fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-7e04-b8e4-d64e183027cc" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019fd749-6b74-7f80-a1c5-e53bf79c67fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-7f80-a1c5-e53bf79c67fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019fd749-6b74-7f80-a1c5-e53bf79c67fa" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-7f80-a1c5-e53bf79c67fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-73c5-abfd-8c9f6dc1a4f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019fd749-6b74-7f80-a1c5-e53bf79c67fa" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-73c5-abfd-8c9f6dc1a4f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019fd749-6b74-7cb5-b82d-e91777484696" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-73c5-abfd-8c9f6dc1a4f8" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019fd749-6b74-7cb5-b82d-e91777484696" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7917-bab1-031940ed4266" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-7e04-b8e4-d64e183027cc" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7917-bab1-031940ed4266" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7917-bab1-031940ed4266_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7917-bab1-031940ed4266" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7917-bab1-031940ed4266_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7e14-b1e4-8d69c033c680" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7917-bab1-031940ed4266" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7e14-b1e4-8d69c033c680" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fd749-6b74-7a76-96df-5b8cfd727874" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7e14-b1e4-8d69c033c680" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fd749-6b74-7a76-96df-5b8cfd727874" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fd749-6b74-7ee8-a364-754d66c7def1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7e14-b1e4-8d69c033c680" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fd749-6b74-7ee8-a364-754d66c7def1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fd749-6b74-7499-8875-04f7338b6ad3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7e14-b1e4-8d69c033c680" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fd749-6b74-7499-8875-04f7338b6ad3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7f42-bdb5-94584b815bfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-7e04-b8e4-d64e183027cc" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7f42-bdb5-94584b815bfc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7f42-bdb5-94584b815bfc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7f42-bdb5-94584b815bfc" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7f42-bdb5-94584b815bfc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-72e7-97cf-39471a0e5593" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7f42-bdb5-94584b815bfc" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-72e7-97cf-39471a0e5593" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019fd749-6b74-774a-800f-64fdeccf3691" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-72e7-97cf-39471a0e5593" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019fd749-6b74-774a-800f-64fdeccf3691" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6b74-7b34-85b8-96bf9a7451d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-72e7-97cf-39471a0e5593" xlink:to="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6b74-7b34-85b8-96bf9a7451d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6b74-7bc2-bf80-219548e593e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-72e7-97cf-39471a0e5593" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6b74-7bc2-bf80-219548e593e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6b74-7008-b8fa-22f7da694fbc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-72e7-97cf-39471a0e5593" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6b74-7008-b8fa-22f7da694fbc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_PooledTrustPreferredSecuritiesMember_019fd749-6b74-700f-a86c-bce8a6ae72b2" xlink:href="onb-20260930.xsd#onb_PooledTrustPreferredSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-72e7-97cf-39471a0e5593" xlink:to="loc_onb_PooledTrustPreferredSecuritiesMember_019fd749-6b74-700f-a86c-bce8a6ae72b2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDebtSecuritiesMember_019fd749-6b74-7a9a-b3a3-4208b04b556b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-72e7-97cf-39471a0e5593" xlink:to="loc_us-gaap_OtherDebtSecuritiesMember_019fd749-6b74-7a9a-b3a3-4208b04b556b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetFairValueNetAbstract_01a0424f-f441-734c-8a8c-e78cb2f96c61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetFairValueNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ddc-bee9-1f49c10d8330" xlink:to="loc_us-gaap_DerivativeAssetFairValueNetAbstract_01a0424f-f441-734c-8a8c-e78cb2f96c61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019fd749-6b74-7abf-8b17-6e6dd16e7d52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetFairValueNetAbstract_01a0424f-f441-734c-8a8c-e78cb2f96c61" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019fd749-6b74-7abf-8b17-6e6dd16e7d52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fd749-6b74-7119-aab4-6f7b28c24eca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetFairValueNetAbstract_01a0424f-f441-734c-8a8c-e78cb2f96c61" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fd749-6b74-7119-aab4-6f7b28c24eca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesHeldForSaleFairValueDisclosure_019fd749-6b74-742b-9f1f-6db971887054" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgagesHeldForSaleFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetFairValueNetAbstract_01a0424f-f441-734c-8a8c-e78cb2f96c61" xlink:to="loc_us-gaap_MortgagesHeldForSaleFairValueDisclosure_019fd749-6b74-742b-9f1f-6db971887054" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019fd749-6b74-7490-9c92-b1e4ded2d13b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetFairValueNetAbstract_01a0424f-f441-734c-8a8c-e78cb2f96c61" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019fd749-6b74-7490-9c92-b1e4ded2d13b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityFairValueNetAbstract_01a0424f-9f41-7f8b-add3-60f9ac05ff91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilityFairValueNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ddc-bee9-1f49c10d8330" xlink:to="loc_us-gaap_DerivativeLiabilityFairValueNetAbstract_01a0424f-9f41-7f8b-add3-60f9ac05ff91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019fd749-6b74-7532-aeee-924ab48f453c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLiabilityFairValueNetAbstract_01a0424f-9f41-7f8b-add3-60f9ac05ff91" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019fd749-6b74-7532-aeee-924ab48f453c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/FAIRVALUEScheduleofAssetsMeasuredatFairValueonaNonRecurringBasisDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#FAIRVALUEScheduleofAssetsMeasuredatFairValueonaNonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/FAIRVALUEScheduleofAssetsMeasuredatFairValueonaNonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b74-755b-af34-cd8982ac443d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7b2c-8ee1-07087d033c75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b74-755b-af34-cd8982ac443d" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7b2c-8ee1-07087d033c75" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b74-71a0-a7a0-167a3c8e626f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7b2c-8ee1-07087d033c75" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b74-71a0-a7a0-167a3c8e626f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-71a0-a7a0-167a3c8e626f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b74-71a0-a7a0-167a3c8e626f" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-71a0-a7a0-167a3c8e626f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b74-7b15-b4dc-cd1059e1f0d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b74-71a0-a7a0-167a3c8e626f" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b74-7b15-b4dc-cd1059e1f0d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-7b56-aa20-369ccd4a7699" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b74-7b15-b4dc-cd1059e1f0d1" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-7b56-aa20-369ccd4a7699" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019fd749-6b74-7744-9863-da33d468217d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-7b56-aa20-369ccd4a7699" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019fd749-6b74-7744-9863-da33d468217d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019fd749-6b74-7fc2-8ab1-16dee671383e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b74-7b56-aa20-369ccd4a7699" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019fd749-6b74-7fc2-8ab1-16dee671383e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019fd749-6b74-72b3-9c73-07a0128fba74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7b2c-8ee1-07087d033c75" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019fd749-6b74-72b3-9c73-07a0128fba74" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-72b3-9c73-07a0128fba74_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019fd749-6b74-72b3-9c73-07a0128fba74" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-72b3-9c73-07a0128fba74_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-7452-ba76-18ee17029fda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019fd749-6b74-72b3-9c73-07a0128fba74" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-7452-ba76-18ee17029fda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsNonrecurringMember_019fd749-6b74-7384-9a02-b4fd4fd4c515" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsNonrecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019fd749-6b74-7452-ba76-18ee17029fda" xlink:to="loc_us-gaap_FairValueMeasurementsNonrecurringMember_019fd749-6b74-7384-9a02-b4fd4fd4c515" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b74-7cd0-964a-7142c3c81272" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7b2c-8ee1-07087d033c75" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b74-7cd0-964a-7142c3c81272" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7cd0-964a-7142c3c81272_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b74-7cd0-964a-7142c3c81272" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7cd0-964a-7142c3c81272_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7386-8a25-f57660645580" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b74-7cd0-964a-7142c3c81272" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7386-8a25-f57660645580" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6b74-7dd3-86ca-85009ebb08d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7386-8a25-f57660645580" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6b74-7dd3-86ca-85009ebb08d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6b74-7739-9abb-48d443596ca7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7386-8a25-f57660645580" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6b74-7739-9abb-48d443596ca7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7fa4-86be-10177734a9dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7b2c-8ee1-07087d033c75" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7fa4-86be-10177734a9dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7fa4-86be-10177734a9dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7fa4-86be-10177734a9dd" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7fa4-86be-10177734a9dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-740b-932c-dd64b5ae44a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7fa4-86be-10177734a9dd" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-740b-932c-dd64b5ae44a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fd749-6b74-7b47-a6b8-59ba4737de24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-740b-932c-dd64b5ae44a0" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fd749-6b74-7b47-a6b8-59ba4737de24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fd749-6b74-71e9-bc06-f2b007ed51d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-740b-932c-dd64b5ae44a0" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fd749-6b74-71e9-bc06-f2b007ed51d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fd749-6b74-729d-9d92-9b00ff437772" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-740b-932c-dd64b5ae44a0" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fd749-6b74-729d-9d92-9b00ff437772" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-757a-9fa1-468ff5e9af67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7b2c-8ee1-07087d033c75" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-757a-9fa1-468ff5e9af67" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-757a-9fa1-468ff5e9af67_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-757a-9fa1-468ff5e9af67" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-757a-9fa1-468ff5e9af67_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7f31-b434-08c0b6a93513" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-757a-9fa1-468ff5e9af67" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7f31-b434-08c0b6a93513" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CommercialRealEstateForeclosedAssetsMember_019fd749-6b74-7c8c-8951-b535f22bf4ad" xlink:href="onb-20260930.xsd#onb_CommercialRealEstateForeclosedAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7f31-b434-08c0b6a93513" xlink:to="loc_onb_CommercialRealEstateForeclosedAssetsMember_019fd749-6b74-7c8c-8951-b535f22bf4ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ResidentialForeclosedAssetsMember_019fd749-6b74-7b35-ad98-2dc45e0830d7" xlink:href="onb-20260930.xsd#onb_ResidentialForeclosedAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7f31-b434-08c0b6a93513" xlink:to="loc_onb_ResidentialForeclosedAssetsMember_019fd749-6b74-7b35-ad98-2dc45e0830d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019fd749-6b74-775a-961d-b3743d0e0ca3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b74-755b-af34-cd8982ac443d" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019fd749-6b74-775a-961d-b3743d0e0ca3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/FAIRVALUEAdditionalInformationDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#FAIRVALUEAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/FAIRVALUEAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-724e-ace6-1243d82874bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-724e-ace6-1243d82874bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-7812-a768-163cab7afe69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fd749-6b74-724e-ace6-1243d82874bd" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-7812-a768-163cab7afe69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7812-a768-163cab7afe69_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-7812-a768-163cab7afe69" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7812-a768-163cab7afe69_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7c96-90c5-f333732ce91e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-7812-a768-163cab7afe69" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7c96-90c5-f333732ce91e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ImpairedCommercialAndCommercialRealEstateLoansMember_019fd749-6b74-7ff2-bc4d-e81e7865bee1" xlink:href="onb-20260930.xsd#onb_ImpairedCommercialAndCommercialRealEstateLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7c96-90c5-f333732ce91e" xlink:to="loc_onb_ImpairedCommercialAndCommercialRealEstateLoansMember_019fd749-6b74-7ff2-bc4d-e81e7865bee1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_PrincipalAmountOfCommercialAndCommercialRealEstateLoans_019fd749-6b74-7c64-ae83-d719a35098fe" xlink:href="onb-20260930.xsd#onb_PrincipalAmountOfCommercialAndCommercialRealEstateLoans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:to="loc_onb_PrincipalAmountOfCommercialAndCommercialRealEstateLoans_019fd749-6b74-7c64-ae83-d719a35098fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForLoanAndLeaseLossesRealEstate_019fd749-6b74-7bf6-8245-d65629fdf2de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForLoanAndLeaseLossesRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:to="loc_us-gaap_AllowanceForLoanAndLeaseLossesRealEstate_019fd749-6b74-7bf6-8245-d65629fdf2de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal_019fd749-6b74-7201-9a89-d4695deaacb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal_019fd749-6b74-7201-9a89-d4695deaacb1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherRealEstateOwnedIncludingRepossessedProperty_019fd749-6b74-76a1-bb64-0d60a6fd89cd" xlink:href="onb-20260930.xsd#onb_OtherRealEstateOwnedIncludingRepossessedProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:to="loc_onb_OtherRealEstateOwnedIncludingRepossessedProperty_019fd749-6b74-76a1-bb64-0d60a6fd89cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_OtherRealEstateOwnedPropertyWriteDown_019fd749-6b74-7cfb-8cd6-3409cafed101" xlink:href="onb-20260930.xsd#onb_OtherRealEstateOwnedPropertyWriteDown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:to="loc_onb_OtherRealEstateOwnedPropertyWriteDown_019fd749-6b74-7cfb-8cd6-3409cafed101" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_PastDuePeriodOfMortgageLoansHeldForSale_019fd749-6b74-73c7-a9b8-f13ea66aaea8" xlink:href="onb-20260930.xsd#onb_PastDuePeriodOfMortgageLoansHeldForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:to="loc_onb_PastDuePeriodOfMortgageLoansHeldForSale_019fd749-6b74-73c7-a9b8-f13ea66aaea8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndFeeIncomeLoansCommercialAndResidentialRealEstate_019fd749-6b74-7c6f-b922-ddbf414c981f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndFeeIncomeLoansCommercialAndResidentialRealEstate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fd749-6b74-7ce9-ac8d-5c6b744c9cee" xlink:to="loc_us-gaap_InterestAndFeeIncomeLoansCommercialAndResidentialRealEstate_019fd749-6b74-7c6f-b922-ddbf414c981f" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/FAIRVALUEScheduleofQuantitativeInformationaboutSignificantUnobservableInputsUsedinFairValueMeasurementsDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#FAIRVALUEScheduleofQuantitativeInformationaboutSignificantUnobservableInputsUsedinFairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/FAIRVALUEScheduleofQuantitativeInformationaboutSignificantUnobservableInputsUsedinFairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b74-75ed-a462-45231c3ec580" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7fa4-9388-50d8154ffb2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b74-75ed-a462-45231c3ec580" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7fa4-9388-50d8154ffb2d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-7778-a5ef-d58f3b80b1a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7fa4-9388-50d8154ffb2d" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-7778-a5ef-d58f3b80b1a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7778-a5ef-d58f3b80b1a9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-7778-a5ef-d58f3b80b1a9" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7778-a5ef-d58f3b80b1a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7854-aba6-b72107a3e966" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019fd749-6b74-7778-a5ef-d58f3b80b1a9" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7854-aba6-b72107a3e966" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CollateralDependentImpairedLoansMember_019fd749-6b74-76c4-85dd-dcbfe4b661f1" xlink:href="onb-20260930.xsd#onb_CollateralDependentImpairedLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7854-aba6-b72107a3e966" xlink:to="loc_onb_CollateralDependentImpairedLoansMember_019fd749-6b74-76c4-85dd-dcbfe4b661f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ForeclosedAssetsMember_019fd749-6b74-7b98-bcde-a5672837bb25" xlink:href="onb-20260930.xsd#onb_ForeclosedAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fd749-6b74-7854-aba6-b72107a3e966" xlink:to="loc_onb_ForeclosedAssetsMember_019fd749-6b74-7b98-bcde-a5672837bb25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7aec-a69b-fe2eb3bb70e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7fa4-9388-50d8154ffb2d" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7aec-a69b-fe2eb3bb70e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7aec-a69b-fe2eb3bb70e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7aec-a69b-fe2eb3bb70e5" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-7aec-a69b-fe2eb3bb70e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-73f4-8b78-63827a13a13b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b74-7aec-a69b-fe2eb3bb70e5" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-73f4-8b78-63827a13a13b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fd749-6b74-74e8-b9d3-8736c3dd089a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b74-73f4-8b78-63827a13a13b" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fd749-6b74-74e8-b9d3-8736c3dd089a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b74-7881-90fb-9123a9fc3972" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7fa4-9388-50d8154ffb2d" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b74-7881-90fb-9123a9fc3972" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7881-90fb-9123a9fc3972_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b74-7881-90fb-9123a9fc3972" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7881-90fb-9123a9fc3972_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7c2e-aaa7-07cf8bba894c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b74-7881-90fb-9123a9fc3972" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7c2e-aaa7-07cf8bba894c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6b74-7441-b65a-414b98148c00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7c2e-aaa7-07cf8bba894c" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6b74-7441-b65a-414b98148c00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6b74-7596-96a5-31b6af1a991d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7c2e-aaa7-07cf8bba894c" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6b74-7596-96a5-31b6af1a991d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6b74-70c8-b8d5-5be887fc8194" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b74-7c2e-aaa7-07cf8bba894c" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6b74-70c8-b8d5-5be887fc8194" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_019fd749-6b74-79b2-b6f9-8b0c9bfcf30a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7fa4-9388-50d8154ffb2d" xlink:to="loc_us-gaap_ValuationTechniqueAxis_019fd749-6b74-79b2-b6f9-8b0c9bfcf30a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019fd749-6b74-79b2-b6f9-8b0c9bfcf30a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019fd749-6b74-79b2-b6f9-8b0c9bfcf30a" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019fd749-6b74-79b2-b6f9-8b0c9bfcf30a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019fd749-6b74-760a-aeee-766e8ef98c7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019fd749-6b74-79b2-b6f9-8b0c9bfcf30a" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019fd749-6b74-760a-aeee-766e8ef98c7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_019fd749-6b74-7a01-b0cb-6fb53013fb5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ValuationTechniqueDiscountedCashFlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019fd749-6b74-760a-aeee-766e8ef98c7c" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_019fd749-6b74-7a01-b0cb-6fb53013fb5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_ValuationTechniqueFairValueOfCollateralMember_019fd749-6b74-7696-9183-dcd46db64496" xlink:href="onb-20260930.xsd#onb_ValuationTechniqueFairValueOfCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019fd749-6b74-760a-aeee-766e8ef98c7c" xlink:to="loc_onb_ValuationTechniqueFairValueOfCollateralMember_019fd749-6b74-7696-9183-dcd46db64496" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fd749-6b74-7ac6-8f76-3a0658ac1bce" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7fa4-9388-50d8154ffb2d" xlink:to="loc_srt_RangeAxis_019fd749-6b74-7ac6-8f76-3a0658ac1bce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-7ac6-8f76-3a0658ac1bce_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019fd749-6b74-7ac6-8f76-3a0658ac1bce" xlink:to="loc_srt_RangeMember_019fd749-6b74-7ac6-8f76-3a0658ac1bce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fd749-6b74-72c4-b309-936acd238641" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019fd749-6b74-7ac6-8f76-3a0658ac1bce" xlink:to="loc_srt_RangeMember_019fd749-6b74-72c4-b309-936acd238641" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fd749-6b74-7de6-9400-bad34c879ebf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-72c4-b309-936acd238641" xlink:to="loc_srt_MinimumMember_019fd749-6b74-7de6-9400-bad34c879ebf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fd749-6b74-75e1-9b7e-e7e24135888f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-72c4-b309-936acd238641" xlink:to="loc_srt_MaximumMember_019fd749-6b74-75e1-9b7e-e7e24135888f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_019fd749-6b74-733e-9aae-2d5e7b598ced" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019fd749-6b74-72c4-b309-936acd238641" xlink:to="loc_srt_WeightedAverageMember_019fd749-6b74-733e-9aae-2d5e7b598ced" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019fd749-6b74-7e3c-87f7-39950eaccc04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b74-7fa4-9388-50d8154ffb2d" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019fd749-6b74-7e3c-87f7-39950eaccc04" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019fd749-6b74-7e3c-87f7-39950eaccc04_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019fd749-6b74-7e3c-87f7-39950eaccc04" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019fd749-6b74-7e3c-87f7-39950eaccc04_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019fd749-6b74-7281-b37d-dde7bc996de6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019fd749-6b74-7e3c-87f7-39950eaccc04" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019fd749-6b74-7281-b37d-dde7bc996de6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019fd749-6b74-7641-99ea-705baed3e788" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019fd749-6b74-7281-b37d-dde7bc996de6" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019fd749-6b74-7641-99ea-705baed3e788" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansHeldForSaleFairValueDisclosure_019fd749-6b74-76a8-ba2b-5294c2682c1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansHeldForSaleFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b74-75ed-a462-45231c3ec580" xlink:to="loc_us-gaap_LoansHeldForSaleFairValueDisclosure_019fd749-6b74-76a8-ba2b-5294c2682c1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansHeldForSaleMeasurementInput_019fd749-6b74-786a-b881-3ee46d207308" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansHeldForSaleMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b74-75ed-a462-45231c3ec580" xlink:to="loc_us-gaap_LoansHeldForSaleMeasurementInput_019fd749-6b74-786a-b881-3ee46d207308" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfRealEstateProperties_019fd749-6b74-7cd7-a6e7-3757c264099c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfRealEstateProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b74-75ed-a462-45231c3ec580" xlink:to="loc_us-gaap_NumberOfRealEstateProperties_019fd749-6b74-7cd7-a6e7-3757c264099c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/FAIRVALUEScheduleofDifferenceBetweentheAggregateFairValueandtheAggregateRemainingPrincipalBalanceDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#FAIRVALUEScheduleofDifferenceBetweentheAggregateFairValueandtheAggregateRemainingPrincipalBalanceDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/FAIRVALUEScheduleofDifferenceBetweentheAggregateFairValueandtheAggregateRemainingPrincipalBalanceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueOptionQuantitativeDisclosuresLineItems_019fd749-6b74-75d6-bf32-70a9df16d07d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueOptionQuantitativeDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueOptionQuantitativeDisclosuresTable_019fd749-6b74-7fec-99de-f5418ddf72bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueOptionQuantitativeDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueOptionQuantitativeDisclosuresLineItems_019fd749-6b74-75d6-bf32-70a9df16d07d" xlink:to="loc_us-gaap_FairValueOptionQuantitativeDisclosuresTable_019fd749-6b74-7fec-99de-f5418ddf72bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7550-8b4f-2f4c5ab87ac3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueOptionQuantitativeDisclosuresTable_019fd749-6b74-7fec-99de-f5418ddf72bd" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7550-8b4f-2f4c5ab87ac3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7550-8b4f-2f4c5ab87ac3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7550-8b4f-2f4c5ab87ac3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7550-8b4f-2f4c5ab87ac3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7f57-8f51-c9947ae15ae7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7550-8b4f-2f4c5ab87ac3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7f57-8f51-c9947ae15ae7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LoansHeldForSaleMember_019fd749-6b74-72c8-b16c-7d57285cee61" xlink:href="onb-20260930.xsd#onb_LoansHeldForSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7f57-8f51-c9947ae15ae7" xlink:to="loc_onb_LoansHeldForSaleMember_019fd749-6b74-72c8-b16c-7d57285cee61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesHeldForSaleFairValueDisclosure_019fd749-6b74-7048-a214-c625ddf6f393" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgagesHeldForSaleFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueOptionQuantitativeDisclosuresLineItems_019fd749-6b74-75d6-bf32-70a9df16d07d" xlink:to="loc_us-gaap_MortgagesHeldForSaleFairValueDisclosure_019fd749-6b74-7048-a214-c625ddf6f393" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueOptionAggregateDifferencesLoansAndLongTermReceivables_019fd749-6b74-7f57-b755-2c23d9e61f2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueOptionAggregateDifferencesLoansAndLongTermReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueOptionQuantitativeDisclosuresLineItems_019fd749-6b74-75d6-bf32-70a9df16d07d" xlink:to="loc_us-gaap_FairValueOptionAggregateDifferencesLoansAndLongTermReceivables_019fd749-6b74-7f57-b755-2c23d9e61f2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableHeldForSaleAmount_019fd749-6b74-7e85-a536-c775f79e6de3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansReceivableHeldForSaleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueOptionQuantitativeDisclosuresLineItems_019fd749-6b74-75d6-bf32-70a9df16d07d" xlink:to="loc_us-gaap_LoansReceivableHeldForSaleAmount_019fd749-6b74-7e85-a536-c775f79e6de3" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/FAIRVALUEScheduleofChangesinFairValueforItemsMeasuredatFairValuePursuanttoElectionoftheFairValueDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#FAIRVALUEScheduleofChangesinFairValueforItemsMeasuredatFairValuePursuanttoElectionoftheFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/FAIRVALUEScheduleofChangesinFairValueforItemsMeasuredatFairValuePursuanttoElectionoftheFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fd749-6b74-7b8c-8804-080f5ea7f227" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_019fd749-6b74-7214-92e1-cf6dd15aa2fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fd749-6b74-7b8c-8804-080f5ea7f227" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_019fd749-6b74-7214-92e1-cf6dd15aa2fa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7087-b781-537496cddb57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_019fd749-6b74-7214-92e1-cf6dd15aa2fa" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7087-b781-537496cddb57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7087-b781-537496cddb57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7087-b781-537496cddb57" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7087-b781-537496cddb57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7803-aa11-1a056403ac23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b74-7087-b781-537496cddb57" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7803-aa11-1a056403ac23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_LoansHeldForSaleMember_019fd749-6b74-77dc-bae7-1015777f72c5" xlink:href="onb-20260930.xsd#onb_LoansHeldForSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b74-7803-aa11-1a056403ac23" xlink:to="loc_onb_LoansHeldForSaleMember_019fd749-6b74-77dc-bae7-1015777f72c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingGainsLosses_019fd749-6b74-718f-bdfb-17a571c14d38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fd749-6b74-7b8c-8804-080f5ea7f227" xlink:to="loc_us-gaap_OtherNonoperatingGainsLosses_019fd749-6b74-718f-bdfb-17a571c14d38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_019fd749-6b74-7a25-953c-cf473de42368" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fd749-6b74-7b8c-8804-080f5ea7f227" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_019fd749-6b74-7a25-953c-cf473de42368" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_019fd749-6b74-72d5-a79d-b206c0c1dbcb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fd749-6b74-7b8c-8804-080f5ea7f227" xlink:to="loc_us-gaap_InterestExpense_019fd749-6b74-72d5-a79d-b206c0c1dbcb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueOptionChangesInFairValueGainLoss1_019fd749-6b74-7e3b-b7ae-234a21bfea66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueOptionChangesInFairValueGainLoss1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fd749-6b74-7b8c-8804-080f5ea7f227" xlink:to="loc_us-gaap_FairValueOptionChangesInFairValueGainLoss1_019fd749-6b74-7e3b-b7ae-234a21bfea66" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.oldnational.com/role/FAIRVALUEScheduleofCarryingAmountsandEstimatedFairValuesofFinancialInstrumentsNotCarriedatFairValueDetails" xlink:type="simple" xlink:href="onb-20260930.xsd#FAIRVALUEScheduleofCarryingAmountsandEstimatedFairValuesofFinancialInstrumentsNotCarriedatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.oldnational.com/role/FAIRVALUEScheduleofCarryingAmountsandEstimatedFairValuesofFinancialInstrumentsNotCarriedatFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b75-76bf-95d2-839d242fc7df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b75-7eed-ae75-0d2e23713d02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b75-76bf-95d2-839d242fc7df" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b75-7eed-ae75-0d2e23713d02" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b75-71d3-8038-5ea5dffd6d30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b75-7eed-ae75-0d2e23713d02" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b75-71d3-8038-5ea5dffd6d30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b75-71d3-8038-5ea5dffd6d30_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b75-71d3-8038-5ea5dffd6d30" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b75-71d3-8038-5ea5dffd6d30_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b75-7750-b0c7-9b36f03bd5af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019fd749-6b75-71d3-8038-5ea5dffd6d30" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b75-7750-b0c7-9b36f03bd5af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b75-7326-bfd5-4b14291a16e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fd749-6b75-7750-b0c7-9b36f03bd5af" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b75-7326-bfd5-4b14291a16e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019fd749-6b75-7b30-835a-e8a0addf6cb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b75-7326-bfd5-4b14291a16e7" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019fd749-6b75-7b30-835a-e8a0addf6cb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019fd749-6b75-781b-8726-b2c1bf0ffdfa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fd749-6b75-7326-bfd5-4b14291a16e7" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019fd749-6b75-781b-8726-b2c1bf0ffdfa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b75-7fd7-9c5e-6e01d9bab147" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b75-7eed-ae75-0d2e23713d02" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b75-7fd7-9c5e-6e01d9bab147" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b75-7fd7-9c5e-6e01d9bab147_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b75-7fd7-9c5e-6e01d9bab147" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b75-7fd7-9c5e-6e01d9bab147_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b75-7c4e-9796-e73708f1298f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fd749-6b75-7fd7-9c5e-6e01d9bab147" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b75-7c4e-9796-e73708f1298f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fd749-6b75-7478-9897-1dfa98f60c96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b75-7c4e-9796-e73708f1298f" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fd749-6b75-7478-9897-1dfa98f60c96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fd749-6b75-748f-90c7-6e1d44db7145" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b75-7c4e-9796-e73708f1298f" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fd749-6b75-748f-90c7-6e1d44db7145" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fd749-6b75-7322-9614-c451caea0b1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fd749-6b75-7c4e-9796-e73708f1298f" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fd749-6b75-7322-9614-c451caea0b1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b75-775d-92ed-618a9dc81b79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b75-7eed-ae75-0d2e23713d02" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b75-775d-92ed-618a9dc81b79" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b75-775d-92ed-618a9dc81b79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b75-775d-92ed-618a9dc81b79" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b75-775d-92ed-618a9dc81b79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b75-7a2d-aec6-bdd577845578" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019fd749-6b75-775d-92ed-618a9dc81b79" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b75-7a2d-aec6-bdd577845578" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6b75-7fe1-b239-600017d41df3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b75-7a2d-aec6-bdd577845578" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019fd749-6b75-7fe1-b239-600017d41df3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6b75-7605-8677-b4e8cce8e5b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b75-7a2d-aec6-bdd577845578" xlink:to="loc_us-gaap_CommercialRealEstatePortfolioSegmentMember_019fd749-6b75-7605-8677-b4e8cce8e5b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6b75-725b-a417-311fe3281361" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b75-7a2d-aec6-bdd577845578" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019fd749-6b75-725b-a417-311fe3281361" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_019fd749-6b75-763f-8ce2-c3f739caedf8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019fd749-6b75-7a2d-aec6-bdd577845578" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_019fd749-6b75-763f-8ce2-c3f739caedf8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b75-7949-93af-660080404256" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fd749-6b75-7eed-ae75-0d2e23713d02" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b75-7949-93af-660080404256" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b75-7949-93af-660080404256_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b75-7949-93af-660080404256" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b75-7949-93af-660080404256_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b75-7326-aa9b-b399d22ca388" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019fd749-6b75-7949-93af-660080404256" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b75-7326-aa9b-b399d22ca388" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6b75-792b-bc86-00a3deb302e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b75-7326-aa9b-b399d22ca388" xlink:to="loc_us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_019fd749-6b75-792b-bc86-00a3deb302e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6b75-7129-9511-15dd37d01ad6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b75-7326-aa9b-b399d22ca388" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_019fd749-6b75-7129-9511-15dd37d01ad6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6b75-737c-bc4f-f5f45c7680e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fd749-6b75-7326-aa9b-b399d22ca388" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fd749-6b75-737c-bc4f-f5f45c7680e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fd749-6b75-7db2-9f58-33b4d0cfa8b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b75-76bf-95d2-839d242fc7df" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fd749-6b75-7db2-9f58-33b4d0cfa8b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fd749-6b75-751f-9ec4-b879fa674a88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fd749-6b75-7db2-9f58-33b4d0cfa8b2" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019fd749-6b75-751f-9ec4-b879fa674a88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostAfterAllowanceForCreditLossAbstract_019fd749-6b75-7502-918e-e550e8b1e793" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostAfterAllowanceForCreditLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fd749-6b75-7db2-9f58-33b4d0cfa8b2" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostAfterAllowanceForCreditLossAbstract_019fd749-6b75-7502-918e-e550e8b1e793" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecurities_019fd749-6b75-74d3-9dce-7907b17da712" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HeldToMaturitySecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostAfterAllowanceForCreditLossAbstract_019fd749-6b75-7502-918e-e550e8b1e793" xlink:to="loc_us-gaap_HeldToMaturitySecurities_019fd749-6b75-74d3-9dce-7907b17da712" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedInterestAfterAllowanceForCreditLossAbstract_019fd749-6b75-7f04-94d0-46c9c2fe37cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedInterestAfterAllowanceForCreditLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fd749-6b75-7db2-9f58-33b4d0cfa8b2" xlink:to="loc_us-gaap_AccruedInterestAfterAllowanceForCreditLossAbstract_019fd749-6b75-7f04-94d0-46c9c2fe37cb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6b75-7aec-83f5-89a4af32e957" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccruedInterestAfterAllowanceForCreditLossAbstract_019fd749-6b75-7f04-94d0-46c9c2fe37cb" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019fd749-6b75-7aec-83f5-89a4af32e957" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivable_019fd749-6b75-7f71-863e-9f294e073430" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fd749-6b75-7db2-9f58-33b4d0cfa8b2" xlink:to="loc_us-gaap_InterestReceivable_019fd749-6b75-7f71-863e-9f294e073430" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b75-76bf-95d2-839d242fc7df" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsAbstract_019fd749-6b75-7423-a176-97fe30c0dd15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:to="loc_us-gaap_DepositsAbstract_019fd749-6b75-7423-a176-97fe30c0dd15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestBearingDepositLiabilitiesDomestic_019fd749-6b75-747e-a80b-a9e77644a4fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestBearingDepositLiabilitiesDomestic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsAbstract_019fd749-6b75-7423-a176-97fe30c0dd15" xlink:to="loc_us-gaap_NoninterestBearingDepositLiabilitiesDomestic_019fd749-6b75-747e-a80b-a9e77644a4fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_CheckingNowSavingsAndMoneyMarketInterestbearingDeposits_019fd749-6b75-7058-9085-e2f7fc037e44" xlink:href="onb-20260930.xsd#onb_CheckingNowSavingsAndMoneyMarketInterestbearingDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsAbstract_019fd749-6b75-7423-a176-97fe30c0dd15" xlink:to="loc_onb_CheckingNowSavingsAndMoneyMarketInterestbearingDeposits_019fd749-6b75-7058-9085-e2f7fc037e44" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeDeposits_019fd749-6b75-74d1-91c4-9ef3165e2f48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimeDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DepositsAbstract_019fd749-6b75-7423-a176-97fe30c0dd15" xlink:to="loc_us-gaap_TimeDeposits_019fd749-6b75-74d1-91c4-9ef3165e2f48" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsPurchased_019fd749-6b75-714d-9c30-bbe9e57d3fea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalFundsPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:to="loc_us-gaap_FederalFundsPurchased_019fd749-6b75-714d-9c30-bbe9e57d3fea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019fd749-6b75-75a0-8b66-067e11fee10f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:to="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchase_019fd749-6b75-75a0-8b66-067e11fee10f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvancesFromFederalHomeLoanBanks_019fd749-6b75-72d6-94b8-5ea9c392208c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdvancesFromFederalHomeLoanBanks"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:to="loc_us-gaap_AdvancesFromFederalHomeLoanBanks_019fd749-6b75-72d6-94b8-5ea9c392208c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherBorrowings_019fd749-6b75-7509-87ee-5bb117bb8b18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:to="loc_us-gaap_OtherBorrowings_019fd749-6b75-7509-87ee-5bb117bb8b18" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrentAndNoncurrent_019fd749-6b75-7f52-aace-aa54eea4c27a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:to="loc_us-gaap_InterestPayableCurrentAndNoncurrent_019fd749-6b75-7f52-aace-aa54eea4c27a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019fd749-6b75-7732-a422-4d7731d11d1f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_019fd749-6b75-7371-b67b-c384360f96ca" xlink:to="loc_us-gaap_LineOfCredit_019fd749-6b75-7732-a422-4d7731d11d1f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_onb_FairValueDisclosureOffBalanceSheetRisksAmountAbstract_019fd749-6b75-7604-a2f8-fd94341ef812" xlink:href="onb-20260930.xsd#onb_FairValueDisclosureOffBalanceSheetRisksAmountAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fd749-6b75-76bf-95d2-839d242fc7df" xlink:to="loc_onb_FairValueDisclosureOffBalanceSheetRisksAmountAbstract_019fd749-6b75-7604-a2f8-fd94341ef812" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability_019fd749-6b75-778e-8a05-57f11c44773b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_onb_FairValueDisclosureOffBalanceSheetRisksAmountAbstract_019fd749-6b75-7604-a2f8-fd94341ef812" xlink:to="loc_us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability_019fd749-6b75-778e-8a05-57f11c44773b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-roles-2026.xsd#eedm1"/>
  <link:definitionLink xlink:role="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest" xlink:type="arc" order="101"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivableAndOtherAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestReceivableAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_InterestReceivableAndOtherAssets" xlink:type="arc" order="102"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization" xlink:type="arc" order="103"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherBorrowings" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract" xlink:to="loc_us-gaap_OtherBorrowings" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfCashFlowsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfCashFlowsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpense" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfCashFlowsAbstract" xlink:to="loc_us-gaap_NoninterestExpense" xlink:type="arc" order="31"/>
  </link:definitionLink>
</link:linkbase>
