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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019fdc15-c0fb-742c-b0b0-9c5c037af04e,g:b3c50b3f-1ea2-4ce6-928b-03c07bcbde82-->
<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.afginc.com/role/Cover" xlink:type="simple" xlink:href="afg-20260930.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019fdc15-c3bd-730b-b355-ae517f0c5ba9" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntitiesTable_019fdc15-c3bd-730b-b355-ae517f0c5ba9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fdc15-c3bd-7def-9796-c0a33919d11f" 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_019fdc15-c3bd-730b-b355-ae517f0c5ba9" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fdc15-c3bd-7def-9796-c0a33919d11f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fdc15-c3bd-7def-9796-c0a33919d11f_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_019fdc15-c3bd-7def-9796-c0a33919d11f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fdc15-c3bd-7def-9796-c0a33919d11f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fdc15-c3bd-732f-bbac-9aba1277e523" 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_019fdc15-c3bd-7def-9796-c0a33919d11f" xlink:to="loc_us-gaap_ClassOfStockDomain_019fdc15-c3bd-732f-bbac-9aba1277e523" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fdc15-c3bd-724c-8ceb-4540bbe38988" 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_019fdc15-c3bd-732f-bbac-9aba1277e523" xlink:to="loc_us-gaap_CommonStockMember_019fdc15-c3bd-724c-8ceb-4540bbe38988" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SubordinatedDebenturesDueInMarch2059Member_019fdc15-c3bd-76f7-931f-8a2a03763fe2" xlink:href="afg-20260930.xsd#afg_SubordinatedDebenturesDueInMarch2059Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fdc15-c3bd-732f-bbac-9aba1277e523" xlink:to="loc_afg_SubordinatedDebenturesDueInMarch2059Member_019fdc15-c3bd-76f7-931f-8a2a03763fe2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SubordinatedDebenturesDueInJune2060Member_019fdc15-c3bd-77ef-8615-fcad68759b52" xlink:href="afg-20260930.xsd#afg_SubordinatedDebenturesDueInJune2060Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fdc15-c3bd-732f-bbac-9aba1277e523" xlink:to="loc_afg_SubordinatedDebenturesDueInJune2060Member_019fdc15-c3bd-77ef-8615-fcad68759b52" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SubordinatedDebenturesdueinDecember2059Member_019fdc15-c3bd-70c8-8260-10241e328aa0" xlink:href="afg-20260930.xsd#afg_SubordinatedDebenturesdueinDecember2059Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fdc15-c3bd-732f-bbac-9aba1277e523" xlink:to="loc_afg_SubordinatedDebenturesdueinDecember2059Member_019fdc15-c3bd-70c8-8260-10241e328aa0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SubordinatedDebenturesDueInSeptember2060Member_019fdc15-c3bd-74ed-a33b-c15cf19f1d89" xlink:href="afg-20260930.xsd#afg_SubordinatedDebenturesDueInSeptember2060Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fdc15-c3bd-732f-bbac-9aba1277e523" xlink:to="loc_afg_SubordinatedDebenturesDueInSeptember2060Member_019fdc15-c3bd-74ed-a33b-c15cf19f1d89" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019fdc15-c3bd-77e1-9b3b-7b0fd1f07f21" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_DocumentType_019fdc15-c3bd-77e1-9b3b-7b0fd1f07f21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019fdc15-c3bd-7271-8126-6242eb4ab96b" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_DocumentQuarterlyReport_019fdc15-c3bd-7271-8126-6242eb4ab96b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019fdc15-c3bd-7c8b-9e3e-3312ae7bbc3c" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_DocumentPeriodEndDate_019fdc15-c3bd-7c8b-9e3e-3312ae7bbc3c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019fdc15-c3bd-70c2-9fd1-37f06a50ed9b" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_DocumentTransitionReport_019fdc15-c3bd-70c2-9fd1-37f06a50ed9b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019fdc15-c3bd-7e75-a5c5-5ecc5086209f" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityFileNumber_019fdc15-c3bd-7e75-a5c5-5ecc5086209f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019fdc15-c3bd-7d02-acea-285aa599484a" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityRegistrantName_019fdc15-c3bd-7d02-acea-285aa599484a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019fdc15-c3bd-7cd8-9bde-626c1d001cc1" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019fdc15-c3bd-7cd8-9bde-626c1d001cc1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019fdc15-c3bd-78f7-9bea-5d793c6efb2f" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityTaxIdentificationNumber_019fdc15-c3bd-78f7-9bea-5d793c6efb2f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019fdc15-c3bd-7bf5-a326-e05070688cd0" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityAddressAddressLine1_019fdc15-c3bd-7bf5-a326-e05070688cd0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019fdc15-c3bd-7184-bfec-6d1a74c462de" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityAddressCityOrTown_019fdc15-c3bd-7184-bfec-6d1a74c462de" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019fdc15-c3bd-7907-88dd-a2b2b0430908" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityAddressStateOrProvince_019fdc15-c3bd-7907-88dd-a2b2b0430908" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019fdc15-c3bd-7d86-81a6-57b558e733b2" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityAddressPostalZipCode_019fdc15-c3bd-7d86-81a6-57b558e733b2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019fdc15-c3bd-7608-957f-7f3e05c107dd" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_CityAreaCode_019fdc15-c3bd-7608-957f-7f3e05c107dd" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019fdc15-c3bd-7a1f-9d9e-7408741e1065" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_LocalPhoneNumber_019fdc15-c3bd-7a1f-9d9e-7408741e1065" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019fdc15-c3bd-78ca-922f-860bd0bdb787" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_Security12bTitle_019fdc15-c3bd-78ca-922f-860bd0bdb787" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019fdc15-c3bd-7e16-a56b-e0055a8abd6c" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_TradingSymbol_019fdc15-c3bd-7e16-a56b-e0055a8abd6c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019fdc15-c3bd-70a0-97c8-39539ba4b762" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_SecurityExchangeName_019fdc15-c3bd-70a0-97c8-39539ba4b762" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019fdc15-c3bd-71f8-8844-accab6c2339b" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityCurrentReportingStatus_019fdc15-c3bd-71f8-8844-accab6c2339b" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019fdc15-c3bd-7644-a3e5-354bb3273308" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityInteractiveDataCurrent_019fdc15-c3bd-7644-a3e5-354bb3273308" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019fdc15-c3bd-777c-ae18-df701891ea5f" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityFilerCategory_019fdc15-c3bd-777c-ae18-df701891ea5f" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019fdc15-c3bd-7303-a533-c7fe56167d49" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntitySmallBusiness_019fdc15-c3bd-7303-a533-c7fe56167d49" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019fdc15-c3bd-754f-8c5e-0dd7a49f8d32" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityEmergingGrowthCompany_019fdc15-c3bd-754f-8c5e-0dd7a49f8d32" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019fdc15-c3bd-7eed-9c6b-02430a4d571f" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityShellCompany_019fdc15-c3bd-7eed-9c6b-02430a4d571f" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019fdc15-c3bd-746a-af25-6a99a5432c51" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019fdc15-c3bd-746a-af25-6a99a5432c51" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019fdc15-c3bd-7c1e-8c0a-dc24b9e7e8b6" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_EntityCentralIndexKey_019fdc15-c3bd-7c1e-8c0a-dc24b9e7e8b6" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019fdc15-c3bd-7b2b-9a42-8d03be0d9307" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_AmendmentFlag_019fdc15-c3bd-7b2b-9a42-8d03be0d9307" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019fdc15-c3bd-766a-bd34-78e100158b6f" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_DocumentFiscalYearFocus_019fdc15-c3bd-766a-bd34-78e100158b6f" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019fdc15-c3bd-7d30-8900-c99b233e6032" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019fdc15-c3bd-7d30-8900-c99b233e6032" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019fdc15-c3bd-7b5c-8fe2-dd6a7f331117" 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_019fdc15-c3bd-7de6-a36b-b0a25187aa7d" xlink:to="loc_dei_CurrentFiscalYearEndDate_019fdc15-c3bd-7b5c-8fe2-dd6a7f331117" xlink:type="arc" order="28"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/ConsolidatedStatementofChangesinEquityUnaudited" xlink:type="simple" xlink:href="afg-20260930.xsd#ConsolidatedStatementofChangesinEquityUnaudited"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/ConsolidatedStatementofChangesinEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019fdc15-c470-7cbe-afa5-261d2e84bcf4" 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_019fdc15-c470-7522-8f36-5335b214b786" 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_019fdc15-c470-7cbe-afa5-261d2e84bcf4" xlink:to="loc_us-gaap_StatementTable_019fdc15-c470-7522-8f36-5335b214b786" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fdc15-c470-775e-88c2-6c262537231f" 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_019fdc15-c470-7522-8f36-5335b214b786" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fdc15-c470-775e-88c2-6c262537231f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fdc15-c470-775e-88c2-6c262537231f_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_019fdc15-c470-775e-88c2-6c262537231f" xlink:to="loc_us-gaap_EquityComponentDomain_019fdc15-c470-775e-88c2-6c262537231f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fdc15-c470-7792-92bc-b9294ab1dbea" 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_019fdc15-c470-775e-88c2-6c262537231f" xlink:to="loc_us-gaap_EquityComponentDomain_019fdc15-c470-7792-92bc-b9294ab1dbea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_019fdc15-c470-7c68-a717-6dcec8e7eeb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019fdc15-c470-7792-92bc-b9294ab1dbea" xlink:to="loc_us-gaap_ParentMember_019fdc15-c470-7c68-a717-6dcec8e7eeb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fdc15-c470-74b1-a10d-b2681e523876" 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_ParentMember_019fdc15-c470-7c68-a717-6dcec8e7eeb8" xlink:to="loc_us-gaap_CommonStockMember_019fdc15-c470-74b1-a10d-b2681e523876" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember_019fdc15-c470-7cc6-8ef7-8283134e7942" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019fdc15-c470-7c68-a717-6dcec8e7eeb8" xlink:to="loc_us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember_019fdc15-c470-7cc6-8ef7-8283134e7942" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019fdc15-c470-7bdd-85a0-e9d16959ce0b" 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_ParentMember_019fdc15-c470-7c68-a717-6dcec8e7eeb8" xlink:to="loc_us-gaap_RetainedEarningsMember_019fdc15-c470-7bdd-85a0-e9d16959ce0b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fdc15-c470-7ad3-9ba0-ed746dc3871a" 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_ParentMember_019fdc15-c470-7c68-a717-6dcec8e7eeb8" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fdc15-c470-7ad3-9ba0-ed746dc3871a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" 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_019fdc15-c470-7cbe-afa5-261d2e84bcf4" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fdc15-c470-7372-aa31-8ed0a7a5495c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019fdc15-c470-7372-aa31-8ed0a7a5495c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fdc15-c470-7255-a4fa-676c1396ed0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fdc15-c470-7255-a4fa-676c1396ed0c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019fdc15-c470-783b-9135-e2466f55e290" 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_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_NetIncomeLoss_019fdc15-c470-783b-9135-e2466f55e290" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019fdc15-c470-712a-a947-33c882937ee9" 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_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019fdc15-c470-712a-a947-33c882937ee9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_019fdc15-c470-78f2-9051-44c912d2d470" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_DividendsCommonStockCash_019fdc15-c470-78f2-9051-44c912d2d470" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:href="afg-20260930.xsd#afg_SharesIssuedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019fdc15-c470-77e6-ac7b-b071d9eff7c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019fdc15-c470-77e6-ac7b-b071d9eff7c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019fdc15-c470-73e7-abe4-3a2fec5d9de5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019fdc15-c470-73e7-abe4-3a2fec5d9de5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019fdc15-c470-7a16-8205-351d08bee348" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019fdc15-c470-7a16-8205-351d08bee348" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeBenefitPlan_019fdc15-c470-7f88-be04-4c1db4e9ad26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeBenefitPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeBenefitPlan_019fdc15-c470-7f88-be04-4c1db4e9ad26" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeBenefitPlan_019fdc15-c470-7f2c-8f68-dac969a029f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeBenefitPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeBenefitPlan_019fdc15-c470-7f2c-8f68-dac969a029f5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan_019fdc15-c470-7be8-a5fe-2a6ad5c93014" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan_019fdc15-c470-7be8-a5fe-2a6ad5c93014" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan_019fdc15-c470-772b-afac-53740e725893" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SharesIssuedAbstract_019fdc15-c470-7f4f-8486-2549b60d1486" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan_019fdc15-c470-772b-afac-53740e725893" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fdc15-c470-77db-8318-cd70d0a56779" 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_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019fdc15-c470-77db-8318-cd70d0a56779" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_019fdc15-c470-7cdf-bd60-8d74ae6d7179" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_019fdc15-c470-7cdf-bd60-8d74ae6d7179" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_019fdc15-c470-7a7f-8d66-3ef19facb3e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_019fdc15-c470-7a7f-8d66-3ef19facb3e3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_StockRepurchasedSharesExchangedInStockCompensationPlansShares_019fdc15-c470-7da5-b608-c1759c0dbe16" xlink:href="afg-20260930.xsd#afg_StockRepurchasedSharesExchangedInStockCompensationPlansShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_afg_StockRepurchasedSharesExchangedInStockCompensationPlansShares_019fdc15-c470-7da5-b608-c1759c0dbe16" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_StockRepurchasedSharesExchangedInStockCompensationPlansValue_019fdc15-c470-76f2-9644-9ab0fa05081c" xlink:href="afg-20260930.xsd#afg_StockRepurchasedSharesExchangedInStockCompensationPlansValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_afg_StockRepurchasedSharesExchangedInStockCompensationPlansValue_019fdc15-c470-76f2-9644-9ab0fa05081c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_019fdc15-c470-7ae1-9e8e-d817fe918c20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019fdc15-c470-7f33-b759-7b4a36922cbe" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_019fdc15-c470-7ae1-9e8e-d817fe918c20" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019fdc15-c470-7495-9cda-5f633b3b3e99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fdc15-c470-7af0-94d8-ce4177abc917" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/AccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#AccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/AccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019fdc15-c470-7a75-98a4-db45bf3c6014" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019fdc15-c470-7a75-98a4-db45bf3c6014" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c470-7944-8868-7e9139f59f58" 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_ScheduleOfVariableInterestEntitiesTable_019fdc15-c470-7a75-98a4-db45bf3c6014" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c470-7944-8868-7e9139f59f58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c470-7944-8868-7e9139f59f58_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_019fdc15-c470-7944-8868-7e9139f59f58" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c470-7944-8868-7e9139f59f58_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c470-7b2a-8aa6-d01b3cdfcc86" 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_019fdc15-c470-7944-8868-7e9139f59f58" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c470-7b2a-8aa6-d01b3cdfcc86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NewCollateralizedLoanObligationTemporaryWarehousingEntitiesMember_019fdc15-c470-7283-94d4-439a06a48b15" xlink:href="afg-20260930.xsd#afg_NewCollateralizedLoanObligationTemporaryWarehousingEntitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c470-7b2a-8aa6-d01b3cdfcc86" xlink:to="loc_afg_NewCollateralizedLoanObligationTemporaryWarehousingEntitiesMember_019fdc15-c470-7283-94d4-439a06a48b15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fdc15-c470-707f-b52d-28739d064ec9" 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_ScheduleOfVariableInterestEntitiesTable_019fdc15-c470-7a75-98a4-db45bf3c6014" xlink:to="loc_srt_RangeAxis_019fdc15-c470-707f-b52d-28739d064ec9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fdc15-c470-707f-b52d-28739d064ec9_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_019fdc15-c470-707f-b52d-28739d064ec9" xlink:to="loc_srt_RangeMember_019fdc15-c470-707f-b52d-28739d064ec9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fdc15-c470-79d9-8f62-44860f69ebb5" 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_019fdc15-c470-707f-b52d-28739d064ec9" xlink:to="loc_srt_RangeMember_019fdc15-c470-79d9-8f62-44860f69ebb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fdc15-c470-7bd6-a5c7-bb7a11a279f4" 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_019fdc15-c470-79d9-8f62-44860f69ebb5" xlink:to="loc_srt_MaximumMember_019fdc15-c470-7bd6-a5c7-bb7a11a279f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_VariableInterestEntityAssets_019fdc15-c470-7876-bf03-22cf0c52dd9e" xlink:href="afg-20260930.xsd#afg_VariableInterestEntityAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_afg_VariableInterestEntityAssets_019fdc15-c470-7876-bf03-22cf0c52dd9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_VariableInterestEntityLiabilities_019fdc15-c470-7811-8c39-3ca7f6866360" xlink:href="afg-20260930.xsd#afg_VariableInterestEntityLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_afg_VariableInterestEntityLiabilities_019fdc15-c470-7811-8c39-3ca7f6866360" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiability_019fdc15-c470-77de-b85c-6a4d4a47e42a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_us-gaap_OperatingLeaseLiability_019fdc15-c470-77de-b85c-6a4d4a47e42a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList_019fdc15-c470-7423-af1d-f7faaf84ed72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_us-gaap_OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList_019fdc15-c470-7423-af1d-f7faaf84ed72" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019fdc15-c470-7ce7-9308-79a1810c950a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019fdc15-c470-7ce7-9308-79a1810c950a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_019fdc15-c470-7874-b090-84840d56f131" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_019fdc15-c470-7874-b090-84840d56f131" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019fdc15-c470-7627-ab74-338957136832" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019fdc15-c470-7627-ab74-338957136832" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019fdc15-c470-73cd-8ad4-1237f6dfe4f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019fdc15-c470-73cd-8ad4-1237f6dfe4f4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_MaturityPeriodOfShortTermInvestmentMaximum_019fdc15-c470-72a4-a54c-8eddc9f23a0b" xlink:href="afg-20260930.xsd#afg_MaturityPeriodOfShortTermInvestmentMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c470-781e-9d3c-ccb0e27d0ce4" xlink:to="loc_afg_MaturityPeriodOfShortTermInvestmentMaximum_019fdc15-c470-72a4-a54c-8eddc9f23a0b" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/SegmentsofOperationsNarrativeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#SegmentsofOperationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/SegmentsofOperationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a01fb5-3651-720c-b206-886e6af23f42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01fb5-3651-7da2-9239-577787a5ab4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01fb5-3651-720c-b206-886e6af23f42" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01fb5-3651-7da2-9239-577787a5ab4a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a01fb5-3651-7532-a780-83cfc2a3f353" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01fb5-3651-7da2-9239-577787a5ab4a" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a01fb5-3651-7532-a780-83cfc2a3f353" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01fb5-3651-7532-a780-83cfc2a3f353_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01fb5-3651-7532-a780-83cfc2a3f353" xlink:to="loc_us-gaap_SegmentDomain_01a01fb5-3651-7532-a780-83cfc2a3f353_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01fb5-3651-765c-a807-0a20a007a054" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01fb5-3651-7532-a780-83cfc2a3f353" xlink:to="loc_us-gaap_SegmentDomain_01a01fb5-3651-765c-a807-0a20a007a054" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_01a01fb5-3651-77c1-947e-ad22c6fe2407" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a01fb5-3651-765c-a807-0a20a007a054" xlink:to="loc_us-gaap_CorporateAndOtherMember_01a01fb5-3651-77c1-947e-ad22c6fe2407" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019fdc15-c470-7c1f-9635-6531199b8561" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01fb5-3651-720c-b206-886e6af23f42" xlink:to="loc_us-gaap_NumberOfReportableSegments_019fdc15-c470-7c1f-9635-6531199b8561" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DisclosureOnGeographicAreasPropertyAndCasualtyRevenuesAttributedToForeignCountries_019fdc15-c470-7bd8-a03d-b30ae62340ee" xlink:href="afg-20260930.xsd#afg_DisclosureOnGeographicAreasPropertyAndCasualtyRevenuesAttributedToForeignCountries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01fb5-3651-720c-b206-886e6af23f42" xlink:to="loc_afg_DisclosureOnGeographicAreasPropertyAndCasualtyRevenuesAttributedToForeignCountries_019fdc15-c470-7bd8-a03d-b30ae62340ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNetPeriodIncreaseDecrease_01a01fb4-efa9-754c-a105-54331db9f71f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNetPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01fb5-3651-720c-b206-886e6af23f42" xlink:to="loc_us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNetPeriodIncreaseDecrease_01a01fb4-efa9-754c-a105-54331db9f71f" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/SegmentsofOperationsAssetsbysegmentDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#SegmentsofOperationsAssetsbysegmentDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/SegmentsofOperationsAssetsbysegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-71a2-bd6d-a2978b524a7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-75c9-a353-e04412d1aab4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-71a2-bd6d-a2978b524a7b" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-75c9-a353-e04412d1aab4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7ceb-8a4b-1f01251129d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-75c9-a353-e04412d1aab4" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7ceb-8a4b-1f01251129d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fdc15-c470-7ceb-8a4b-1f01251129d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7ceb-8a4b-1f01251129d5" xlink:to="loc_us-gaap_SegmentDomain_019fdc15-c470-7ceb-8a4b-1f01251129d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fdc15-c470-7b97-818b-54af4e8f953f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7ceb-8a4b-1f01251129d5" xlink:to="loc_us-gaap_SegmentDomain_019fdc15-c470-7b97-818b-54af4e8f953f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PropertyAndCasualtyInsuranceMember_019fdc15-c470-7d49-b333-5d12c836a479" xlink:href="afg-20260930.xsd#afg_PropertyAndCasualtyInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fdc15-c470-7b97-818b-54af4e8f953f" xlink:to="loc_afg_PropertyAndCasualtyInsuranceMember_019fdc15-c470-7d49-b333-5d12c836a479" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019fdc15-c470-7e16-8273-18cb3fba019f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fdc15-c470-7b97-818b-54af4e8f953f" xlink:to="loc_us-gaap_CorporateAndOtherMember_019fdc15-c470-7e16-8273-18cb3fba019f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019fdc15-c470-79dd-96aa-ecef5fb78b35" 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_SegmentReportingInformationLineItems_019fdc15-c470-71a2-bd6d-a2978b524a7b" xlink:to="loc_us-gaap_Assets_019fdc15-c470-79dd-96aa-ecef5fb78b35" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/SegmentsofOperationsRevenuesbysegmentandsubsegmentDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#SegmentsofOperationsRevenuesbysegmentandsubsegmentDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/SegmentsofOperationsRevenuesbysegmentandsubsegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-759c-b117-4504cf2a8fa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-759c-b117-4504cf2a8fa7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019fdc15-c470-741c-bba3-03e239f4e620" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-759c-b117-4504cf2a8fa7" xlink:to="loc_srt_ConsolidationItemsAxis_019fdc15-c470-741c-bba3-03e239f4e620" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fdc15-c470-741c-bba3-03e239f4e620_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019fdc15-c470-741c-bba3-03e239f4e620" xlink:to="loc_srt_ConsolidationItemsDomain_019fdc15-c470-741c-bba3-03e239f4e620_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fdc15-c470-78a9-9f1a-e76a2fa0d9b2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019fdc15-c470-741c-bba3-03e239f4e620" xlink:to="loc_srt_ConsolidationItemsDomain_019fdc15-c470-78a9-9f1a-e76a2fa0d9b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019fdc15-c470-791e-a073-59f6e0c2683e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fdc15-c470-78a9-9f1a-e76a2fa0d9b2" xlink:to="loc_us-gaap_OperatingSegmentsMember_019fdc15-c470-791e-a073-59f6e0c2683e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7707-8c54-4b01e0a33ce2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-759c-b117-4504cf2a8fa7" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7707-8c54-4b01e0a33ce2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fdc15-c470-7707-8c54-4b01e0a33ce2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7707-8c54-4b01e0a33ce2" xlink:to="loc_us-gaap_SegmentDomain_019fdc15-c470-7707-8c54-4b01e0a33ce2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fdc15-c470-7d4c-aec1-cc9175c6ae4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7707-8c54-4b01e0a33ce2" xlink:to="loc_us-gaap_SegmentDomain_019fdc15-c470-7d4c-aec1-cc9175c6ae4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PropertyAndCasualtyInsuranceMember_019fdc15-c470-7d0e-8042-dc3de52f9ad2" xlink:href="afg-20260930.xsd#afg_PropertyAndCasualtyInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fdc15-c470-7d4c-aec1-cc9175c6ae4e" xlink:to="loc_afg_PropertyAndCasualtyInsuranceMember_019fdc15-c470-7d0e-8042-dc3de52f9ad2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019fdc15-c470-7b15-8554-c5730afd238c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fdc15-c470-7d4c-aec1-cc9175c6ae4e" xlink:to="loc_us-gaap_CorporateAndOtherMember_019fdc15-c470-7b15-8554-c5730afd238c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-75fb-b05c-b83ef87e2863" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-759c-b117-4504cf2a8fa7" xlink:to="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-75fb-b05c-b83ef87e2863" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-75fb-b05c-b83ef87e2863_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-75fb-b05c-b83ef87e2863" xlink:to="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-75fb-b05c-b83ef87e2863_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-7a0c-aeeb-e9ddf0cbfd58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-75fb-b05c-b83ef87e2863" xlink:to="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-7a0c-aeeb-e9ddf0cbfd58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyPropertyAndTransportationInsuranceMember_019fdc15-c470-7735-ae61-4cb3daadf3b7" xlink:href="afg-20260930.xsd#afg_SpecialtyPropertyAndTransportationInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-7a0c-aeeb-e9ddf0cbfd58" xlink:to="loc_afg_SpecialtyPropertyAndTransportationInsuranceMember_019fdc15-c470-7735-ae61-4cb3daadf3b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyCasualtyInsuranceMember_019fdc15-c470-7d29-8067-8a7252050229" xlink:href="afg-20260930.xsd#afg_SpecialtyCasualtyInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-7a0c-aeeb-e9ddf0cbfd58" xlink:to="loc_afg_SpecialtyCasualtyInsuranceMember_019fdc15-c470-7d29-8067-8a7252050229" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyFinancialInsuranceMember_019fdc15-c470-71f5-a567-5d06753e1095" xlink:href="afg-20260930.xsd#afg_SpecialtyFinancialInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-7a0c-aeeb-e9ddf0cbfd58" xlink:to="loc_afg_SpecialtyFinancialInsuranceMember_019fdc15-c470-71f5-a567-5d06753e1095" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_01a1892d-ccba-77d4-839c-55735801a392" 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_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-759c-b117-4504cf2a8fa7" xlink:to="loc_us-gaap_InvestmentTypeAxis_01a1892d-ccba-77d4-839c-55735801a392" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_01a1892d-ccba-77d4-839c-55735801a392_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_01a1892d-ccba-77d4-839c-55735801a392" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_01a1892d-ccba-77d4-839c-55735801a392_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_01a1892d-ccba-7094-8820-ba5551754f17" 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_01a1892d-ccba-77d4-839c-55735801a392" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_01a1892d-ccba-7094-8820-ba5551754f17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_CharlestonHarborResortMarinaMember_01a1892d-ccba-7c62-a162-3ccd25d644b9" xlink:href="afg-20260930.xsd#afg_CharlestonHarborResortMarinaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_01a1892d-ccba-7094-8820-ba5551754f17" xlink:to="loc_afg_CharlestonHarborResortMarinaMember_01a1892d-ccba-7c62-a162-3ccd25d644b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsEarnedNet_019fdc15-c470-7484-90e5-9ba442015887" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PremiumsEarnedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_us-gaap_PremiumsEarnedNet_019fdc15-c470-7484-90e5-9ba442015887" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019fdc15-c470-74d3-9b3b-a2b6836f2cae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_us-gaap_NetInvestmentIncome_019fdc15-c470-74d3-9b3b-a2b6836f2cae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIncome_019fdc15-c470-76e0-87df-9a80ab15c61d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_us-gaap_OtherIncome_019fdc15-c470-76e0-87df-9a80ab15c61d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_RevenuesBeforeRealizedGainsLosses_019fdc15-c470-7b6b-ace7-050f357bd964" xlink:href="afg-20260930.xsd#afg_RevenuesBeforeRealizedGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_afg_RevenuesBeforeRealizedGainsLosses_019fdc15-c470-7b6b-ace7-050f357bd964" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_019fdc15-c470-7b69-bd5d-03b18698237a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtAndEquitySecuritiesRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_019fdc15-c470-7b69-bd5d-03b18698237a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_RealizedGainsLossesOnSubsidiaries_01a19fa5-00ef-7e3c-9567-a546173b13ee" xlink:href="afg-20260930.xsd#afg_RealizedGainsLossesOnSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_afg_RealizedGainsLossesOnSubsidiaries_01a19fa5-00ef-7e3c-9567-a546173b13ee" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019fdc15-c470-72ce-b162-2dd190676649" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_us-gaap_Revenues_019fdc15-c470-72ce-b162-2dd190676649" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_01a1892d-ccba-78d6-b3cf-1b9527d4d8de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-7935-8195-51920c40d419" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_01a1892d-ccba-78d6-b3cf-1b9527d4d8de" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/SegmentsofOperationsEarningsbeforeincometaxesbysegmentandsubsegmentDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#SegmentsofOperationsEarningsbeforeincometaxesbysegmentandsubsegmentDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/SegmentsofOperationsEarningsbeforeincometaxesbysegmentandsubsegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-79cf-bd84-e8d4b2fa9191" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7508-85a2-5e30af020198" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-79cf-bd84-e8d4b2fa9191" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7508-85a2-5e30af020198" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019fdc15-c470-7767-b011-b2cb2f5664f8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7508-85a2-5e30af020198" xlink:to="loc_srt_ConsolidationItemsAxis_019fdc15-c470-7767-b011-b2cb2f5664f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fdc15-c470-7767-b011-b2cb2f5664f8_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019fdc15-c470-7767-b011-b2cb2f5664f8" xlink:to="loc_srt_ConsolidationItemsDomain_019fdc15-c470-7767-b011-b2cb2f5664f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fdc15-c470-72ca-ac7d-c7825c8ad76d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019fdc15-c470-7767-b011-b2cb2f5664f8" xlink:to="loc_srt_ConsolidationItemsDomain_019fdc15-c470-72ca-ac7d-c7825c8ad76d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019fdc15-c470-7711-9606-862431488844" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fdc15-c470-72ca-ac7d-c7825c8ad76d" xlink:to="loc_us-gaap_OperatingSegmentsMember_019fdc15-c470-7711-9606-862431488844" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-725d-affb-a8fdaa924dd7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7508-85a2-5e30af020198" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-725d-affb-a8fdaa924dd7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fdc15-c470-725d-affb-a8fdaa924dd7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-725d-affb-a8fdaa924dd7" xlink:to="loc_us-gaap_SegmentDomain_019fdc15-c470-725d-affb-a8fdaa924dd7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fdc15-c470-728c-98bc-d487e842cc1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-725d-affb-a8fdaa924dd7" xlink:to="loc_us-gaap_SegmentDomain_019fdc15-c470-728c-98bc-d487e842cc1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PropertyAndCasualtyInsuranceMember_019fdc15-c470-7238-a6c7-14bd5280776d" xlink:href="afg-20260930.xsd#afg_PropertyAndCasualtyInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fdc15-c470-728c-98bc-d487e842cc1a" xlink:to="loc_afg_PropertyAndCasualtyInsuranceMember_019fdc15-c470-7238-a6c7-14bd5280776d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019fdc15-c470-73f6-97cf-98e64e5eeac8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fdc15-c470-728c-98bc-d487e842cc1a" xlink:to="loc_us-gaap_CorporateAndOtherMember_019fdc15-c470-73f6-97cf-98e64e5eeac8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-79f6-861e-c094acd85b70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7508-85a2-5e30af020198" xlink:to="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-79f6-861e-c094acd85b70" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-79f6-861e-c094acd85b70_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-79f6-861e-c094acd85b70" xlink:to="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-79f6-861e-c094acd85b70_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-72f3-8e2c-1d9a9560ae60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-79f6-861e-c094acd85b70" xlink:to="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-72f3-8e2c-1d9a9560ae60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyPropertyAndTransportationInsuranceMember_019fdc15-c470-7ad3-a5d4-b484a140db61" xlink:href="afg-20260930.xsd#afg_SpecialtyPropertyAndTransportationInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-72f3-8e2c-1d9a9560ae60" xlink:to="loc_afg_SpecialtyPropertyAndTransportationInsuranceMember_019fdc15-c470-7ad3-a5d4-b484a140db61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyCasualtyInsuranceMember_019fdc15-c470-723d-a53d-a6a53c50b4cc" xlink:href="afg-20260930.xsd#afg_SpecialtyCasualtyInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-72f3-8e2c-1d9a9560ae60" xlink:to="loc_afg_SpecialtyCasualtyInsuranceMember_019fdc15-c470-723d-a53d-a6a53c50b4cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyFinancialInsuranceMember_019fdc15-c470-7af7-807b-e898f3374fe4" xlink:href="afg-20260930.xsd#afg_SpecialtyFinancialInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-72f3-8e2c-1d9a9560ae60" xlink:to="loc_afg_SpecialtyFinancialInsuranceMember_019fdc15-c470-7af7-807b-e898f3374fe4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_OtherLinesMember_019fdc15-c470-7542-a8f0-018087a66286" xlink:href="afg-20260930.xsd#afg_OtherLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-72f3-8e2c-1d9a9560ae60" xlink:to="loc_afg_OtherLinesMember_019fdc15-c470-7542-a8f0-018087a66286" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PropertyAndCasualtyInsuranceUnderwritingIncomeLoss_019fdc15-c470-74ac-b440-7a7686950917" xlink:href="afg-20260930.xsd#afg_PropertyAndCasualtyInsuranceUnderwritingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-79cf-bd84-e8d4b2fa9191" xlink:to="loc_afg_PropertyAndCasualtyInsuranceUnderwritingIncomeLoss_019fdc15-c470-74ac-b440-7a7686950917" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_InvestmentAndOtherIncomeNet_019fdc15-c470-7fea-8b89-aa8a3b1263fa" xlink:href="afg-20260930.xsd#afg_InvestmentAndOtherIncomeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-79cf-bd84-e8d4b2fa9191" xlink:to="loc_afg_InvestmentAndOtherIncomeNet_019fdc15-c470-7fea-8b89-aa8a3b1263fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_OperatingIncomeLossBeforeRealizedGainsLossesAndIncomeTaxes_019fdc15-c470-7381-9323-adfcf3c4e0c2" xlink:href="afg-20260930.xsd#afg_OperatingIncomeLossBeforeRealizedGainsLossesAndIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-79cf-bd84-e8d4b2fa9191" xlink:to="loc_afg_OperatingIncomeLossBeforeRealizedGainsLossesAndIncomeTaxes_019fdc15-c470-7381-9323-adfcf3c4e0c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_019fdc15-c470-7a7d-9f13-8077ca958cc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtAndEquitySecuritiesRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-79cf-bd84-e8d4b2fa9191" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_019fdc15-c470-7a7d-9f13-8077ca958cc0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_RealizedGainsLossesOnSubsidiaries_01a19fa5-f181-7467-a515-b656d11d74eb" xlink:href="afg-20260930.xsd#afg_RealizedGainsLossesOnSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-79cf-bd84-e8d4b2fa9191" xlink:to="loc_afg_RealizedGainsLossesOnSubsidiaries_01a19fa5-f181-7467-a515-b656d11d74eb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019fdc15-c470-7eeb-bb26-dac1bd8d3d45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-79cf-bd84-e8d4b2fa9191" xlink:to="loc_us-gaap_OperatingIncomeLoss_019fdc15-c470-7eeb-bb26-dac1bd8d3d45" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/SegmentsofOperationsComponentsofunderwritingprofitincludingsignificantsegmentexpensesbysegmentandsubsegmentDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#SegmentsofOperationsComponentsofunderwritingprofitincludingsignificantsegmentexpensesbysegmentandsubsegmentDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/SegmentsofOperationsComponentsofunderwritingprofitincludingsignificantsegmentexpensesbysegmentandsubsegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-713b-b2f5-9b214eed3bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7854-bef3-0977e4b3c73e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-713b-b2f5-9b214eed3bf6" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7854-bef3-0977e4b3c73e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019fdc15-c470-7a72-bfd6-c8faff7d4b90" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7854-bef3-0977e4b3c73e" xlink:to="loc_srt_ConsolidationItemsAxis_019fdc15-c470-7a72-bfd6-c8faff7d4b90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fdc15-c470-7a72-bfd6-c8faff7d4b90_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019fdc15-c470-7a72-bfd6-c8faff7d4b90" xlink:to="loc_srt_ConsolidationItemsDomain_019fdc15-c470-7a72-bfd6-c8faff7d4b90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019fdc15-c470-783c-91e4-aec4cb27022a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019fdc15-c470-7a72-bfd6-c8faff7d4b90" xlink:to="loc_srt_ConsolidationItemsDomain_019fdc15-c470-783c-91e4-aec4cb27022a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019fdc15-c470-7ff5-9987-e7ab17648e60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019fdc15-c470-783c-91e4-aec4cb27022a" xlink:to="loc_us-gaap_OperatingSegmentsMember_019fdc15-c470-7ff5-9987-e7ab17648e60" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-71a6-92a1-b8d53e9d2b70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7854-bef3-0977e4b3c73e" xlink:to="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-71a6-92a1-b8d53e9d2b70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-71a6-92a1-b8d53e9d2b70_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-71a6-92a1-b8d53e9d2b70" xlink:to="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-71a6-92a1-b8d53e9d2b70_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-73de-869f-4a86a370538a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019fdc15-c470-71a6-92a1-b8d53e9d2b70" xlink:to="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-73de-869f-4a86a370538a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyPropertyAndTransportationInsuranceMember_019fdc15-c470-7e29-81e4-5275d646e460" xlink:href="afg-20260930.xsd#afg_SpecialtyPropertyAndTransportationInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-73de-869f-4a86a370538a" xlink:to="loc_afg_SpecialtyPropertyAndTransportationInsuranceMember_019fdc15-c470-7e29-81e4-5275d646e460" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyCasualtyInsuranceMember_019fdc15-c470-7958-9ab6-369e629cc712" xlink:href="afg-20260930.xsd#afg_SpecialtyCasualtyInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-73de-869f-4a86a370538a" xlink:to="loc_afg_SpecialtyCasualtyInsuranceMember_019fdc15-c470-7958-9ab6-369e629cc712" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SpecialtyFinancialInsuranceMember_019fdc15-c470-7ea7-b5ba-7ff4b3fceef0" xlink:href="afg-20260930.xsd#afg_SpecialtyFinancialInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-73de-869f-4a86a370538a" xlink:to="loc_afg_SpecialtyFinancialInsuranceMember_019fdc15-c470-7ea7-b5ba-7ff4b3fceef0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_OtherLinesMember_019fdc15-c470-776b-896c-0071774f58ca" xlink:href="afg-20260930.xsd#afg_OtherLinesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019fdc15-c470-73de-869f-4a86a370538a" xlink:to="loc_afg_OtherLinesMember_019fdc15-c470-776b-896c-0071774f58ca" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7135-9f94-caa9fcfe535f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019fdc15-c470-7854-bef3-0977e4b3c73e" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7135-9f94-caa9fcfe535f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fdc15-c470-7135-9f94-caa9fcfe535f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7135-9f94-caa9fcfe535f" xlink:to="loc_us-gaap_SegmentDomain_019fdc15-c470-7135-9f94-caa9fcfe535f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019fdc15-c470-75c0-8b1d-dea6a4659c6e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019fdc15-c470-7135-9f94-caa9fcfe535f" xlink:to="loc_us-gaap_SegmentDomain_019fdc15-c470-75c0-8b1d-dea6a4659c6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PropertyAndCasualtyInsuranceMember_019fdc15-c470-7925-8421-445e24909fc7" xlink:href="afg-20260930.xsd#afg_PropertyAndCasualtyInsuranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019fdc15-c470-75c0-8b1d-dea6a4659c6e" xlink:to="loc_afg_PropertyAndCasualtyInsuranceMember_019fdc15-c470-7925-8421-445e24909fc7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PremiumsEarnedNet_019fdc15-c470-79ea-aba2-9a3de1f78241" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PremiumsEarnedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-713b-b2f5-9b214eed3bf6" xlink:to="loc_us-gaap_PremiumsEarnedNet_019fdc15-c470-79ea-aba2-9a3de1f78241" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_019fdc15-c470-7918-a45a-30e7141887f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PolicyholderBenefitsAndClaimsIncurredNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-713b-b2f5-9b214eed3bf6" xlink:to="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_019fdc15-c470-7918-a45a-30e7141887f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019fdc15-c470-7a58-9fbc-fa6b1e0d3ea6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-713b-b2f5-9b214eed3bf6" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019fdc15-c470-7a58-9fbc-fa6b1e0d3ea6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PropertyAndCasualtyInsuranceUnderwritingIncomeLoss_019fdc15-c470-74de-beef-414e0e52acdd" xlink:href="afg-20260930.xsd#afg_PropertyAndCasualtyInsuranceUnderwritingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019fdc15-c470-713b-b2f5-9b214eed3bf6" xlink:to="loc_afg_PropertyAndCasualtyInsuranceUnderwritingIncomeLoss_019fdc15-c470-74de-beef-414e0e52acdd" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/FairValueMeasurementsAssetsandliabilitiesmeasuredandcarriedatfairvalueinthefinancialstatementsDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#FairValueMeasurementsAssetsandliabilitiesmeasuredandcarriedatfairvalueinthefinancialstatementsDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/FairValueMeasurementsAssetsandliabilitiesmeasuredandcarriedatfairvalueinthefinancialstatementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fdc15-c470-7b93-b9cc-7e0f5958685c" 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_019fdc15-c470-7e33-b062-98494b7a6d6d" 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_019fdc15-c470-7b93-b9cc-7e0f5958685c" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fdc15-c470-72cb-858b-85f7c7371a22" 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_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fdc15-c470-72cb-858b-85f7c7371a22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c470-72cb-858b-85f7c7371a22_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_019fdc15-c470-72cb-858b-85f7c7371a22" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c470-72cb-858b-85f7c7371a22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c470-7d32-baef-c2cf4e68327f" 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_019fdc15-c470-72cb-858b-85f7c7371a22" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c470-7d32-baef-c2cf4e68327f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fdc15-c470-7165-a04a-1b0e6c95e8e5" 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_019fdc15-c470-7d32-baef-c2cf4e68327f" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fdc15-c470-7165-a04a-1b0e6c95e8e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fdc15-c470-7b0b-8082-b115f069265d" 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_019fdc15-c470-7d32-baef-c2cf4e68327f" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fdc15-c470-7b0b-8082-b115f069265d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fdc15-c470-7f97-a37f-965083550309" 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_019fdc15-c470-7d32-baef-c2cf4e68327f" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fdc15-c470-7f97-a37f-965083550309" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019fdc15-c470-7057-b0cf-72501a76e93d" 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_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019fdc15-c470-7057-b0cf-72501a76e93d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-7057-b0cf-72501a76e93d_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_019fdc15-c470-7057-b0cf-72501a76e93d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-7057-b0cf-72501a76e93d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" 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_019fdc15-c470-7057-b0cf-72501a76e93d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019fdc15-c470-7ede-8c69-299679b8e423" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019fdc15-c470-7ede-8c69-299679b8e423" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c470-738b-9404-cf1419d7b1a5" 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_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c470-738b-9404-cf1419d7b1a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fdc15-c470-75cb-958d-4f580ef7212f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fdc15-c470-75cb-958d-4f580ef7212f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c470-70c8-aaad-635a91ebb88f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c470-70c8-aaad-635a91ebb88f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c470-771d-86ed-7924d9da87a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollateralizedLoanObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c470-771d-86ed-7924d9da87a0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c470-76b0-8e58-3aae9875e493" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c470-76b0-8e58-3aae9875e493" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c470-7280-aef1-403a3eab6c13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c470-7280-aef1-403a3eab6c13" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019fdc15-c470-7d8f-a1c2-2313aee719a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" xlink:to="loc_us-gaap_EquitySecuritiesMember_019fdc15-c470-7d8f-a1c2-2313aee719a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFinancialInstrumentsAssetsMember_019fdc15-c470-727a-9e92-47b00c17baeb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFinancialInstrumentsAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" xlink:to="loc_us-gaap_DerivativeFinancialInstrumentsAssetsMember_019fdc15-c470-727a-9e92-47b00c17baeb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c470-7725-a78e-a516e7b38cb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c470-7725-a78e-a516e7b38cb3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-7725-a78e-a516e7b38cb3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c470-7725-a78e-a516e7b38cb3" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-7725-a78e-a516e7b38cb3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-724e-897d-6bc52223076c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c470-7725-a78e-a516e7b38cb3" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-724e-897d-6bc52223076c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_019fdc15-c470-77db-b6a3-3778ca21fcda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-724e-897d-6bc52223076c" xlink:to="loc_us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_019fdc15-c470-77db-b6a3-3778ca21fcda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019fdc15-c470-7c08-b8e3-229db9a69dfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationBalanceAxis_019fdc15-c470-7c08-b8e3-229db9a69dfc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_019fdc15-c470-79ba-b2fb-36353d00f373" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fdc15-c470-7b93-b9cc-7e0f5958685c" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_019fdc15-c470-79ba-b2fb-36353d00f373" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_019fdc15-c470-79ba-b2fb-36353d00f373" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c470-714f-a63b-96697212c2c4" 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_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c470-714f-a63b-96697212c2c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradingSecuritiesDebt_019fdc15-c470-7a4d-9fb7-8c86f6c14630" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradingSecuritiesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_TradingSecuritiesDebt_019fdc15-c470-7a4d-9fb7-8c86f6c14630" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019fdc15-c470-7141-a840-c94476791ba8" 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_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019fdc15-c470-7141-a840-c94476791ba8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_VariableInterestEntityAssets_019fdc15-c470-7df9-b6a5-b4e5088f36d0" xlink:href="afg-20260930.xsd#afg_VariableInterestEntityAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_afg_VariableInterestEntityAssets_019fdc15-c470-7df9-b6a5-b4e5088f36d0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssets_019fdc15-c470-729c-bceb-347bd06b64da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_OtherAssets_019fdc15-c470-729c-bceb-347bd06b64da" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019fdc15-c470-76eb-9caa-3d1e181a0e7f" 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_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019fdc15-c470-76eb-9caa-3d1e181a0e7f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_019fdc15-c470-79ba-b2fb-36353d00f373" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019fdc15-c471-7011-a9f1-937a5a1833a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019fdc15-c471-7011-a9f1-937a5a1833a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_VariableInterestEntityLiabilities_019fdc15-c471-7e01-8f95-3e2fc23b9bcd" xlink:href="afg-20260930.xsd#afg_VariableInterestEntityLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:to="loc_afg_VariableInterestEntityLiabilities_019fdc15-c471-7e01-8f95-3e2fc23b9bcd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilities_019fdc15-c471-708e-b1c8-9c48c7048f8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:to="loc_us-gaap_OtherLiabilities_019fdc15-c471-708e-b1c8-9c48c7048f8f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019fdc15-c471-74b1-a696-1c0fdab95885" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019fdc15-c471-74b1-a696-1c0fdab95885" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/FairValueMeasurementsAssetsandliabilitiesmeasuredandcarriedatfairvalueinthefinancialstatementsDetails_1" xlink:type="simple" xlink:href="afg-20260930.xsd#FairValueMeasurementsAssetsandliabilitiesmeasuredandcarriedatfairvalueinthefinancialstatementsDetails_1"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/FairValueMeasurementsAssetsandliabilitiesmeasuredandcarriedatfairvalueinthefinancialstatementsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fdc15-c470-7b93-b9cc-7e0f5958685c" 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_019fdc15-c470-7e33-b062-98494b7a6d6d" 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_019fdc15-c470-7b93-b9cc-7e0f5958685c" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fdc15-c470-72cb-858b-85f7c7371a22" 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_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fdc15-c470-72cb-858b-85f7c7371a22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c470-72cb-858b-85f7c7371a22_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_019fdc15-c470-72cb-858b-85f7c7371a22" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c470-72cb-858b-85f7c7371a22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c470-7d32-baef-c2cf4e68327f" 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_019fdc15-c470-72cb-858b-85f7c7371a22" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c470-7d32-baef-c2cf4e68327f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fdc15-c470-7165-a04a-1b0e6c95e8e5" 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_019fdc15-c470-7d32-baef-c2cf4e68327f" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fdc15-c470-7165-a04a-1b0e6c95e8e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fdc15-c470-7b0b-8082-b115f069265d" 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_019fdc15-c470-7d32-baef-c2cf4e68327f" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fdc15-c470-7b0b-8082-b115f069265d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fdc15-c470-7f97-a37f-965083550309" 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_019fdc15-c470-7d32-baef-c2cf4e68327f" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fdc15-c470-7f97-a37f-965083550309" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019fdc15-c470-7057-b0cf-72501a76e93d" 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_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019fdc15-c470-7057-b0cf-72501a76e93d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-7057-b0cf-72501a76e93d_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_019fdc15-c470-7057-b0cf-72501a76e93d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-7057-b0cf-72501a76e93d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" 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_019fdc15-c470-7057-b0cf-72501a76e93d" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019fdc15-c470-7ede-8c69-299679b8e423" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019fdc15-c470-7ede-8c69-299679b8e423" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c470-738b-9404-cf1419d7b1a5" 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_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c470-738b-9404-cf1419d7b1a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fdc15-c470-75cb-958d-4f580ef7212f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fdc15-c470-75cb-958d-4f580ef7212f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c470-70c8-aaad-635a91ebb88f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c470-70c8-aaad-635a91ebb88f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c470-771d-86ed-7924d9da87a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollateralizedLoanObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c470-771d-86ed-7924d9da87a0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c470-76b0-8e58-3aae9875e493" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c470-76b0-8e58-3aae9875e493" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c470-7280-aef1-403a3eab6c13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c470-775c-b3fb-ad4207347de1" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c470-7280-aef1-403a3eab6c13" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019fdc15-c470-7d8f-a1c2-2313aee719a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" xlink:to="loc_us-gaap_EquitySecuritiesMember_019fdc15-c470-7d8f-a1c2-2313aee719a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFinancialInstrumentsAssetsMember_019fdc15-c470-727a-9e92-47b00c17baeb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFinancialInstrumentsAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c470-77ae-9b61-9f3e66e37086" xlink:to="loc_us-gaap_DerivativeFinancialInstrumentsAssetsMember_019fdc15-c470-727a-9e92-47b00c17baeb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c470-7725-a78e-a516e7b38cb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019fdc15-c470-7e33-b062-98494b7a6d6d" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c470-7725-a78e-a516e7b38cb3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-7725-a78e-a516e7b38cb3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c470-7725-a78e-a516e7b38cb3" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-7725-a78e-a516e7b38cb3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-724e-897d-6bc52223076c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c470-7725-a78e-a516e7b38cb3" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-724e-897d-6bc52223076c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_019fdc15-c470-77db-b6a3-3778ca21fcda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c470-724e-897d-6bc52223076c" xlink:to="loc_us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_019fdc15-c470-77db-b6a3-3778ca21fcda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_019fdc15-c470-79ba-b2fb-36353d00f373" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019fdc15-c470-7b93-b9cc-7e0f5958685c" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_019fdc15-c470-79ba-b2fb-36353d00f373" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_019fdc15-c470-79ba-b2fb-36353d00f373" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c470-714f-a63b-96697212c2c4" 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_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c470-714f-a63b-96697212c2c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradingSecuritiesDebt_019fdc15-c470-7a4d-9fb7-8c86f6c14630" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradingSecuritiesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_TradingSecuritiesDebt_019fdc15-c470-7a4d-9fb7-8c86f6c14630" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019fdc15-c470-7141-a840-c94476791ba8" 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_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019fdc15-c470-7141-a840-c94476791ba8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_VariableInterestEntityAssets_019fdc15-c470-7df9-b6a5-b4e5088f36d0" xlink:href="afg-20260930.xsd#afg_VariableInterestEntityAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_afg_VariableInterestEntityAssets_019fdc15-c470-7df9-b6a5-b4e5088f36d0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssets_019fdc15-c470-729c-bceb-347bd06b64da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_OtherAssets_019fdc15-c470-729c-bceb-347bd06b64da" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019fdc15-c470-76eb-9caa-3d1e181a0e7f" 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_AssetsFairValueDisclosureAbstract_019fdc15-c470-7afd-bf18-26a68a9268e8" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019fdc15-c470-76eb-9caa-3d1e181a0e7f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_019fdc15-c470-79ba-b2fb-36353d00f373" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019fdc15-c471-7011-a9f1-937a5a1833a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019fdc15-c471-7011-a9f1-937a5a1833a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_VariableInterestEntityLiabilities_019fdc15-c471-7e01-8f95-3e2fc23b9bcd" xlink:href="afg-20260930.xsd#afg_VariableInterestEntityLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:to="loc_afg_VariableInterestEntityLiabilities_019fdc15-c471-7e01-8f95-3e2fc23b9bcd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilities_019fdc15-c471-708e-b1c8-9c48c7048f8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:to="loc_us-gaap_OtherLiabilities_019fdc15-c471-708e-b1c8-9c48c7048f8f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019fdc15-c471-74b1-a696-1c0fdab95885" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019fdc15-c471-77b4-a533-27a492becbb8" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019fdc15-c471-74b1-a696-1c0fdab95885" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/FairValueMeasurementsChangesinbalancesofLevel3financialassetscarriedatfairvalueDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#FairValueMeasurementsChangesinbalancesofLevel3financialassetscarriedatfairvalueDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/FairValueMeasurementsChangesinbalancesofLevel3financialassetscarriedatfairvalueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fdc15-c471-7ab2-81b3-5692b9ab9253" 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_019fdc15-c471-788d-9a83-aeb0afcb61a4" 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_019fdc15-c471-7ab2-81b3-5692b9ab9253" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fdc15-c471-788d-9a83-aeb0afcb61a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019fdc15-c471-7b60-bd6d-39d1ba4a05ac" 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_019fdc15-c471-788d-9a83-aeb0afcb61a4" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019fdc15-c471-7b60-bd6d-39d1ba4a05ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c471-7b60-bd6d-39d1ba4a05ac_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_019fdc15-c471-7b60-bd6d-39d1ba4a05ac" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c471-7b60-bd6d-39d1ba4a05ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c471-77cc-a65b-8c385210bc48" 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_019fdc15-c471-7b60-bd6d-39d1ba4a05ac" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c471-77cc-a65b-8c385210bc48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-76c9-83da-c77ffee3c3b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c471-77cc-a65b-8c385210bc48" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-76c9-83da-c77ffee3c3b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c471-7cd1-92db-0846b16e28cb" 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_FixedMaturitiesMember_019fdc15-c471-76c9-83da-c77ffee3c3b4" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c471-7cd1-92db-0846b16e28cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c471-7da4-97cf-0471335fc043" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-76c9-83da-c77ffee3c3b4" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c471-7da4-97cf-0471335fc043" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c471-7f70-b31f-a4b875c2dd8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-76c9-83da-c77ffee3c3b4" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c471-7f70-b31f-a4b875c2dd8f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c471-78aa-82c1-a3ac7b4bff2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-76c9-83da-c77ffee3c3b4" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c471-78aa-82c1-a3ac7b4bff2c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_TradingFixedMaturitiesMember_019fdc15-c471-7949-889a-d624683ded34" xlink:href="afg-20260930.xsd#afg_TradingFixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c471-77cc-a65b-8c385210bc48" xlink:to="loc_afg_TradingFixedMaturitiesMember_019fdc15-c471-7949-889a-d624683ded34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-75be-9468-dc389c0935a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c471-77cc-a65b-8c385210bc48" xlink:to="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-75be-9468-dc389c0935a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AssetsOfManagedInvestmentEntitiesMember_019fdc15-c471-71f2-950c-2aefcfc2cbeb" xlink:href="afg-20260930.xsd#afg_AssetsOfManagedInvestmentEntitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019fdc15-c471-77cc-a65b-8c385210bc48" xlink:to="loc_afg_AssetsOfManagedInvestmentEntitiesMember_019fdc15-c471-71f2-950c-2aefcfc2cbeb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fdc15-c471-7ab2-81b3-5692b9ab9253" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019fdc15-c471-7755-a380-64737ca4925e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019fdc15-c471-7755-a380-64737ca4925e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019fdc15-c471-7864-b0cc-04a4f1d2b4e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019fdc15-c471-7864-b0cc-04a4f1d2b4e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_019fdc15-c471-774b-9dca-4696a97d1082" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_019fdc15-c471-774b-9dca-4696a97d1082" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_019fdc15-c471-70f8-b382-81f76fc12213" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_019fdc15-c471-70f8-b382-81f76fc12213" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_019fdc15-c471-7d68-9c6d-ffe7c4c9f34b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales_019fdc15-c471-7d68-9c6d-ffe7c4c9f34b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_019fdc15-c471-7fd5-8164-e7c938f1126c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_019fdc15-c471-7fd5-8164-e7c938f1126c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_019fdc15-c471-77f1-a804-4b18fd43ad0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7e3c-835c-8769aa8b60aa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_019fdc15-c471-77f1-a804-4b18fd43ad0f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019fdc15-c471-76a8-8247-3fc19cb24880" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/FairValueMeasurementsChangesinbalancesofLevel3financialliabilitiescarriedatfairvalueDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#FairValueMeasurementsChangesinbalancesofLevel3financialliabilitiescarriedatfairvalueDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/FairValueMeasurementsChangesinbalancesofLevel3financialliabilitiescarriedatfairvalueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fdc15-c471-7abc-a4c6-706eab697e45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fdc15-c471-79a7-805d-8001a2236862" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fdc15-c471-7abc-a4c6-706eab697e45" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fdc15-c471-79a7-805d-8001a2236862" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c471-792a-9dd2-28c582df77f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019fdc15-c471-79a7-805d-8001a2236862" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c471-792a-9dd2-28c582df77f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c471-792a-9dd2-28c582df77f7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c471-792a-9dd2-28c582df77f7" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c471-792a-9dd2-28c582df77f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c471-7feb-863d-4a0ccda87e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019fdc15-c471-792a-9dd2-28c582df77f7" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c471-7feb-863d-4a0ccda87e3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_ContingentConsiderationAcquisitionsMember_019fdc15-c471-76ee-9e7c-f95227807f98" xlink:href="afg-20260930.xsd#afg_ContingentConsiderationAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019fdc15-c471-7feb-863d-4a0ccda87e3b" xlink:to="loc_afg_ContingentConsiderationAcquisitionsMember_019fdc15-c471-76ee-9e7c-f95227807f98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019fdc15-c471-7abc-a4c6-706eab697e45" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019fdc15-c471-75a3-ba80-ee1b4e625232" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019fdc15-c471-75a3-ba80-ee1b4e625232" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019fdc15-c471-7779-ac05-e611527b074e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019fdc15-c471-7779-ac05-e611527b074e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome_019fdc15-c471-785e-88cd-04a0c05699ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome_019fdc15-c471-785e-88cd-04a0c05699ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_019fdc15-c471-794b-aee1-f70055af90c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_019fdc15-c471-794b-aee1-f70055af90c1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_019fdc15-c471-7729-8c1c-b0885b488523" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_019fdc15-c471-7729-8c1c-b0885b488523" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersIntoLevel3_019fdc15-c471-7248-bcbc-e0007ee9f0f2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersIntoLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersIntoLevel3_019fdc15-c471-7248-bcbc-e0007ee9f0f2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3_019fdc15-c471-772e-8113-c2d7fa40758e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019fdc15-c471-7a03-866c-0886bc15d069" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3_019fdc15-c471-772e-8113-c2d7fa40758e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019fdc15-c471-7f44-bf8c-4af3cee6f89f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/FairValueMeasurementsThecarryingvalueandfairvalueoffinancialinstrumentsDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#FairValueMeasurementsThecarryingvalueandfairvalueoffinancialinstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/FairValueMeasurementsThecarryingvalueandfairvalueoffinancialinstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019fdc15-c471-748e-99a8-e2de1e5b3429" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019fdc15-c471-7cac-9956-fd9eda387ed2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019fdc15-c471-748e-99a8-e2de1e5b3429" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019fdc15-c471-7cac-9956-fd9eda387ed2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019fdc15-c471-7b5a-8a4f-343ed936796d" 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_FairValueByBalanceSheetGroupingTable_019fdc15-c471-7cac-9956-fd9eda387ed2" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019fdc15-c471-7b5a-8a4f-343ed936796d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fdc15-c471-7b5a-8a4f-343ed936796d_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_019fdc15-c471-7b5a-8a4f-343ed936796d" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fdc15-c471-7b5a-8a4f-343ed936796d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fdc15-c471-71e9-b55c-35ebbf83d134" 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_019fdc15-c471-7b5a-8a4f-343ed936796d" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019fdc15-c471-71e9-b55c-35ebbf83d134" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fdc15-c471-7ee5-9a12-9c26685243a2" 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_019fdc15-c471-71e9-b55c-35ebbf83d134" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019fdc15-c471-7ee5-9a12-9c26685243a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019fdc15-c471-78b5-b0af-0aa7f844a74b" 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_019fdc15-c471-7ee5-9a12-9c26685243a2" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019fdc15-c471-78b5-b0af-0aa7f844a74b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019fdc15-c471-7b55-8860-7815835a26eb" 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_019fdc15-c471-7ee5-9a12-9c26685243a2" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019fdc15-c471-7b55-8860-7815835a26eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fdc15-c471-7114-bc13-9c0a1c35460d" 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_FairValueByBalanceSheetGroupingTable_019fdc15-c471-7cac-9956-fd9eda387ed2" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019fdc15-c471-7114-bc13-9c0a1c35460d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c471-7114-bc13-9c0a1c35460d_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_019fdc15-c471-7114-bc13-9c0a1c35460d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c471-7114-bc13-9c0a1c35460d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c471-7563-8de6-69a636f89274" 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_019fdc15-c471-7114-bc13-9c0a1c35460d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019fdc15-c471-7563-8de6-69a636f89274" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019fdc15-c471-7328-99a1-b04e798cb94c" 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_019fdc15-c471-7563-8de6-69a636f89274" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019fdc15-c471-7328-99a1-b04e798cb94c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019fdc15-c471-7f94-8075-1b739e10416b" 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_019fdc15-c471-7563-8de6-69a636f89274" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019fdc15-c471-7f94-8075-1b739e10416b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019fdc15-c471-73b3-9f89-84774462e825" 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_019fdc15-c471-7563-8de6-69a636f89274" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019fdc15-c471-73b3-9f89-84774462e825" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_FinancialInstrumentsFinancialAssetsAndLiabilitiesBalanceSheetGroupingsAbstract_019fdc15-c471-7ea1-8a4b-a9b638bafc19" xlink:href="afg-20260930.xsd#afg_FinancialInstrumentsFinancialAssetsAndLiabilitiesBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019fdc15-c471-748e-99a8-e2de1e5b3429" xlink:to="loc_afg_FinancialInstrumentsFinancialAssetsAndLiabilitiesBalanceSheetGroupingsAbstract_019fdc15-c471-7ea1-8a4b-a9b638bafc19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fdc15-c471-7611-b079-1ff51915d166" 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_afg_FinancialInstrumentsFinancialAssetsAndLiabilitiesBalanceSheetGroupingsAbstract_019fdc15-c471-7ea1-8a4b-a9b638bafc19" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fdc15-c471-7611-b079-1ff51915d166" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019fdc15-c471-7de6-b8b6-d31aeec4419c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fdc15-c471-7611-b079-1ff51915d166" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019fdc15-c471-7de6-b8b6-d31aeec4419c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019fdc15-c471-77da-923b-74eb398e89c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fdc15-c471-7611-b079-1ff51915d166" xlink:to="loc_us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet_019fdc15-c471-77da-923b-74eb398e89c9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019fdc15-c471-74d7-ac46-4ab965249f19" 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_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_019fdc15-c471-7611-b079-1ff51915d166" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019fdc15-c471-74d7-ac46-4ab965249f19" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019fdc15-c471-7e9e-845e-5245db0ab0c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_FinancialInstrumentsFinancialAssetsAndLiabilitiesBalanceSheetGroupingsAbstract_019fdc15-c471-7ea1-8a4b-a9b638bafc19" xlink:to="loc_us-gaap_LongTermDebt_019fdc15-c471-7e9e-845e-5245db0ab0c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019fdc15-c471-7c57-bd5e-94b3ae125614" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_FinancialInstrumentsFinancialAssetsAndLiabilitiesBalanceSheetGroupingsAbstract_019fdc15-c471-7ea1-8a4b-a9b638bafc19" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019fdc15-c471-7c57-bd5e-94b3ae125614" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsAvailableforsalefixedmaturitiesDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsAvailableforsalefixedmaturitiesDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsAvailableforsalefixedmaturitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7c9d-bf94-28d5c214c281" 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_019fdc15-c471-71e4-9063-079134e8b802" 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_019fdc15-c471-7c9d-bf94-28d5c214c281" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fdc15-c471-71e4-9063-079134e8b802" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-777a-954d-69ee6635cd00" 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_019fdc15-c471-71e4-9063-079134e8b802" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-777a-954d-69ee6635cd00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-777a-954d-69ee6635cd00_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_019fdc15-c471-777a-954d-69ee6635cd00" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-777a-954d-69ee6635cd00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-75f7-9487-885bcd13d451" 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_019fdc15-c471-777a-954d-69ee6635cd00" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-75f7-9487-885bcd13d451" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-75f7-9487-885bcd13d451" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019fdc15-c471-74f9-8bc9-1e87e54ba0c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019fdc15-c471-74f9-8bc9-1e87e54ba0c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c471-7be3-aa3e-f62dff0a2e1c" 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_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c471-7be3-aa3e-f62dff0a2e1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fdc15-c471-7ead-9d1a-e3578bc5706d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fdc15-c471-7ead-9d1a-e3578bc5706d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c471-786b-95d1-e267713f1f57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c471-786b-95d1-e267713f1f57" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c471-72b7-b4ce-47701d6f98ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollateralizedLoanObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:to="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c471-72b7-b4ce-47701d6f98ae" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c471-78df-8f48-e4345cc99c24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c471-78df-8f48-e4345cc99c24" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c471-7093-aaef-cb61c8743290" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f47-a52b-dadcabca3c83" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c471-7093-aaef-cb61c8743290" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019fdc15-c471-7827-8881-25db63620f25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7c9d-bf94-28d5c214c281" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019fdc15-c471-7827-8881-25db63620f25" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019fdc15-c471-7324-ae24-0884ec74ef69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7c9d-bf94-28d5c214c281" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019fdc15-c471-7324-ae24-0884ec74ef69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019fdc15-c471-74ad-94f6-d366d86aada2" 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_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7c9d-bf94-28d5c214c281" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019fdc15-c471-74ad-94f6-d366d86aada2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fdc15-c471-709b-a2be-f1ac4721aaaf" 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_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7c9d-bf94-28d5c214c281" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fdc15-c471-709b-a2be-f1ac4721aaaf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAccumulatedGrossUnrealizedGainLossBeforeTax_019fdc15-c471-7917-8d5c-fb41c643da79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAccumulatedGrossUnrealizedGainLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7c9d-bf94-28d5c214c281" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAccumulatedGrossUnrealizedGainLossBeforeTax_019fdc15-c471-7917-8d5c-fb41c643da79" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c471-7fe0-b1de-9b9d3d5afb70" 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_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7c9d-bf94-28d5c214c281" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c471-7fe0-b1de-9b9d3d5afb70" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsEquitysecuritiesreportedatfairvalueDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsEquitysecuritiesreportedatfairvalueDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsEquitysecuritiesreportedatfairvalueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fdc15-c471-74c4-8bcc-adeafc4ce752" 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_019fdc15-c471-7679-9f37-3792ba6a3e55" 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_019fdc15-c471-74c4-8bcc-adeafc4ce752" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_019fdc15-c471-7679-9f37-3792ba6a3e55" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7af8-914d-7fa787823a71" 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_019fdc15-c471-7679-9f37-3792ba6a3e55" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7af8-914d-7fa787823a71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7af8-914d-7fa787823a71_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_019fdc15-c471-7af8-914d-7fa787823a71" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7af8-914d-7fa787823a71_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-71a7-85e8-dc96194eb27e" 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_019fdc15-c471-7af8-914d-7fa787823a71" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-71a7-85e8-dc96194eb27e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-7b3b-9ff0-f46ec6a66cad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-71a7-85e8-dc96194eb27e" xlink:to="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-7b3b-9ff0-f46ec6a66cad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019fdc15-c471-7da0-bd07-462be950e484" 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_EquitySecuritiesMember_019fdc15-c471-7b3b-9ff0-f46ec6a66cad" xlink:to="loc_us-gaap_CommonStockMember_019fdc15-c471-7da0-bd07-462be950e484" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_019fdc15-c471-7d3f-94a2-c6d7a4287a6c" 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_EquitySecuritiesMember_019fdc15-c471-7b3b-9ff0-f46ec6a66cad" xlink:to="loc_us-gaap_PreferredStockMember_019fdc15-c471-7d3f-94a2-c6d7a4287a6c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCost_019fdc15-c471-73ad-bdae-a6782581fc8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNiCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fdc15-c471-74c4-8bcc-adeafc4ce752" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCost_019fdc15-c471-73ad-bdae-a6782581fc8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_019fdc15-c471-7035-a5d7-e35a1bdd6c15" 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_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fdc15-c471-74c4-8bcc-adeafc4ce752" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_019fdc15-c471-7035-a5d7-e35a1bdd6c15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_EquitySecuritiesFVNIFairValueinExcessofCost_019fdc15-c471-7986-9d7b-0a4220bda2bf" xlink:href="afg-20260930.xsd#afg_EquitySecuritiesFVNIFairValueinExcessofCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_019fdc15-c471-74c4-8bcc-adeafc4ce752" xlink:to="loc_afg_EquitySecuritiesFVNIFairValueinExcessofCost_019fdc15-c471-7986-9d7b-0a4220bda2bf" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsDetailofequitymethodinvestmentsDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsDetailofequitymethodinvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsDetailofequitymethodinvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-7b35-97cb-206de57bff34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_019fdc15-c471-7348-b33b-90289ff13df5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-7b35-97cb-206de57bff34" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_019fdc15-c471-7348-b33b-90289ff13df5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fdc15-c471-7a7a-8907-bb896d92fc9a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019fdc15-c471-7348-b33b-90289ff13df5" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fdc15-c471-7a7a-8907-bb896d92fc9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019fdc15-c471-7a7a-8907-bb896d92fc9a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fdc15-c471-7a7a-8907-bb896d92fc9a" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019fdc15-c471-7a7a-8907-bb896d92fc9a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019fdc15-c471-77d5-bfa4-5d45b2ff3509" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019fdc15-c471-7a7a-8907-bb896d92fc9a" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019fdc15-c471-77d5-bfa4-5d45b2ff3509" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_EquityMethodInvestmentsRealEstateRelatedInvestmentsMember_019fdc15-c471-7fb8-894a-7c6c85e01d91" xlink:href="afg-20260930.xsd#afg_EquityMethodInvestmentsRealEstateRelatedInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019fdc15-c471-77d5-bfa4-5d45b2ff3509" xlink:to="loc_afg_EquityMethodInvestmentsRealEstateRelatedInvestmentsMember_019fdc15-c471-7fb8-894a-7c6c85e01d91" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_EquityMethodInvestmentsPrivateEquityFundsMember_019fdc15-c471-7f28-a8da-eafb93c31291" xlink:href="afg-20260930.xsd#afg_EquityMethodInvestmentsPrivateEquityFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019fdc15-c471-77d5-bfa4-5d45b2ff3509" xlink:to="loc_afg_EquityMethodInvestmentsPrivateEquityFundsMember_019fdc15-c471-7f28-a8da-eafb93c31291" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_EquityMethodInvestmentsPrivateDebtFundsMember_019fdc15-c471-7ff6-a248-5da173b9dd8d" xlink:href="afg-20260930.xsd#afg_EquityMethodInvestmentsPrivateDebtFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019fdc15-c471-77d5-bfa4-5d45b2ff3509" xlink:to="loc_afg_EquityMethodInvestmentsPrivateDebtFundsMember_019fdc15-c471-7ff6-a248-5da173b9dd8d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_019fdc15-c471-7396-8aaa-5372a89efd09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-7b35-97cb-206de57bff34" xlink:to="loc_us-gaap_EquityMethodInvestments_019fdc15-c471-7396-8aaa-5372a89efd09" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019fdc15-c471-7f50-bad4-d35538261d3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-7b35-97cb-206de57bff34" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019fdc15-c471-7f50-bad4-d35538261d3f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsNarrativeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_019fdc15-c471-7b0b-8b82-41cd5d3f720d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_019fdc15-c471-7b0b-8b82-41cd5d3f720d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-727e-b6cc-38c493a9931e" 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_ScheduleOfInvestmentsTable_019fdc15-c471-7b0b-8b82-41cd5d3f720d" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-727e-b6cc-38c493a9931e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-727e-b6cc-38c493a9931e_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_019fdc15-c471-727e-b6cc-38c493a9931e" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-727e-b6cc-38c493a9931e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7ae2-83c6-c9aabb62c5bc" 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_019fdc15-c471-727e-b6cc-38c493a9931e" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7ae2-83c6-c9aabb62c5bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7974-8f78-4df983076ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7ae2-83c6-c9aabb62c5bc" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7974-8f78-4df983076ef2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019fdc15-c471-723a-840d-21c45688303a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_019fdc15-c471-7b0b-8b82-41cd5d3f720d" xlink:to="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019fdc15-c471-723a-840d-21c45688303a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019fdc15-c471-723a-840d-21c45688303a_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019fdc15-c471-723a-840d-21c45688303a" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019fdc15-c471-723a-840d-21c45688303a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019fdc15-c471-7139-b108-e5b9e48eb291" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MortgageLoansOnRealEstateNamePropertyTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis_019fdc15-c471-723a-840d-21c45688303a" xlink:to="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019fdc15-c471-7139-b108-e5b9e48eb291" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_019fdc15-c471-7c5c-9e79-cf9dd3bc050f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_MortgageLoansOnRealEstateNamePropertyTypeDomain_019fdc15-c471-7139-b108-e5b9e48eb291" xlink:to="loc_srt_MultifamilyMember_019fdc15-c471-7c5c-9e79-cf9dd3bc050f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_RealEstateRelatedInvestmentsPercentByPropertyType_019fdc15-c471-7ce6-ae30-621a277cfe47" xlink:href="afg-20260930.xsd#afg_RealEstateRelatedInvestmentsPercentByPropertyType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:to="loc_afg_RealEstateRelatedInvestmentsPercentByPropertyType_019fdc15-c471-7ce6-ae30-621a277cfe47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_UnfundedCommitmentsToLimitedPartnerships_019fdc15-c471-72b3-a0c5-3523a0d51a24" xlink:href="afg-20260930.xsd#afg_UnfundedCommitmentsToLimitedPartnerships"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:to="loc_afg_UnfundedCommitmentsToLimitedPartnerships_019fdc15-c471-72b3-a0c5-3523a0d51a24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fdc15-c471-7566-9b78-ebb2992f654b" 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_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019fdc15-c471-7566-9b78-ebb2992f654b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019fdc15-c471-76c7-842b-9364e4a0d73d" 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_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019fdc15-c471-76c7-842b-9364e4a0d73d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PercentageBasedOnUnrealizedLossOfAvailableForSaleFixedMaturitiesThatAreInUnrealizedLossPositionAndRatedInvestmentGrade_019fdc15-c471-7206-b75f-aaf325709405" xlink:href="afg-20260930.xsd#afg_PercentageBasedOnUnrealizedLossOfAvailableForSaleFixedMaturitiesThatAreInUnrealizedLossPositionAndRatedInvestmentGrade"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:to="loc_afg_PercentageBasedOnUnrealizedLossOfAvailableForSaleFixedMaturitiesThatAreInUnrealizedLossPositionAndRatedInvestmentGrade_019fdc15-c471-7206-b75f-aaf325709405" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PercentageBasedOnFairValueOfAvailableForSaleFixedMaturitiesThatAreInUnrealizedLossPositionAndRatedInvestmentGrade_019fdc15-c471-7505-8e86-754e1701b1c0" xlink:href="afg-20260930.xsd#afg_PercentageBasedOnFairValueOfAvailableForSaleFixedMaturitiesThatAreInUnrealizedLossPositionAndRatedInvestmentGrade"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:to="loc_afg_PercentageBasedOnFairValueOfAvailableForSaleFixedMaturitiesThatAreInUnrealizedLossPositionAndRatedInvestmentGrade_019fdc15-c471-7505-8e86-754e1701b1c0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_MortgageLoanReceivedAsConsiderationForSaleOfRealEstatePrincipalAmount_01a18926-1402-7a16-991e-c389386b3a17" xlink:href="afg-20260930.xsd#afg_MortgageLoanReceivedAsConsiderationForSaleOfRealEstatePrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_019fdc15-c471-75a8-a511-e78af55e600a" xlink:to="loc_afg_MortgageLoanReceivedAsConsiderationForSaleOfRealEstatePrincipalAmount_01a18926-1402-7a16-991e-c389386b3a17" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsGrossunrealizedlossesonsecuritiesbyinvestmentcategoryandlengthoftimethathavebeeninacontinuousunrealizedlosspositionDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsGrossunrealizedlossesonsecuritiesbyinvestmentcategoryandlengthoftimethathavebeeninacontinuousunrealizedlosspositionDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsGrossunrealizedlossesonsecuritiesbyinvestmentcategoryandlengthoftimethathavebeeninacontinuousunrealizedlosspositionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7764-bb76-1a553d660c79" 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_019fdc15-c471-733f-938a-5221b445ea2a" 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_019fdc15-c471-7764-bb76-1a553d660c79" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fdc15-c471-733f-938a-5221b445ea2a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7455-b739-403e6a68bec1" 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_019fdc15-c471-733f-938a-5221b445ea2a" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7455-b739-403e6a68bec1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7455-b739-403e6a68bec1_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_019fdc15-c471-7455-b739-403e6a68bec1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7455-b739-403e6a68bec1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-78d8-a613-94c31f0b753d" 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_019fdc15-c471-7455-b739-403e6a68bec1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-78d8-a613-94c31f0b753d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-78d8-a613-94c31f0b753d" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019fdc15-c471-7ed8-a11b-c9d14cbca4c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019fdc15-c471-7ed8-a11b-c9d14cbca4c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c471-7731-91b1-46f32b351d5a" 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_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_019fdc15-c471-7731-91b1-46f32b351d5a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fdc15-c471-7571-be8e-e96ad376b7f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_019fdc15-c471-7571-be8e-e96ad376b7f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c471-79af-93a8-c03718897eab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_019fdc15-c471-79af-93a8-c03718897eab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c471-72c1-a12e-d9f22fa7c02b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollateralizedLoanObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:to="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c471-72c1-a12e-d9f22fa7c02b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c471-785f-8be6-26ccbf0618cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_019fdc15-c471-785f-8be6-26ccbf0618cb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c471-7246-91b6-3fa107b8bc87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7f1f-bc91-78b1d1279765" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c471-7246-91b6-3fa107b8bc87" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fdc15-c471-7cd0-8716-5528b405522e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7764-bb76-1a553d660c79" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fdc15-c471-7cd0-8716-5528b405522e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019fdc15-c471-71ab-af67-ff6eee45478b" 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_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fdc15-c471-7cd0-8716-5528b405522e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019fdc15-c471-71ab-af67-ff6eee45478b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019fdc15-c471-70b9-b6c1-5512eda8e06a" 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_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fdc15-c471-7cd0-8716-5528b405522e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_019fdc15-c471-70b9-b6c1-5512eda8e06a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValueAsPercentageOfCost_019fdc15-c471-703e-942e-ca729036c1f1" xlink:href="afg-20260930.xsd#afg_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValueAsPercentageOfCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fdc15-c471-7cd0-8716-5528b405522e" xlink:to="loc_afg_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValueAsPercentageOfCost_019fdc15-c471-703e-942e-ca729036c1f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fdc15-c471-711d-ae03-48ee56fbd629" 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_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fdc15-c471-7cd0-8716-5528b405522e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019fdc15-c471-711d-ae03-48ee56fbd629" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019fdc15-c471-719c-8682-ecb820103340" 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_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fdc15-c471-7cd0-8716-5528b405522e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_019fdc15-c471-719c-8682-ecb820103340" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValueAsPercentageOfCost_019fdc15-c471-7a89-bfc4-544039442efd" xlink:href="afg-20260930.xsd#afg_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValueAsPercentageOfCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_019fdc15-c471-7cd0-8716-5528b405522e" xlink:to="loc_afg_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValueAsPercentageOfCost_019fdc15-c471-7a89-bfc4-544039442efd" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsAllowanceforcreditlossesonfixedmaturitiesDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsAllowanceforcreditlossesonfixedmaturitiesDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsAllowanceforcreditlossesonfixedmaturitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossLineItems_019fdc15-c471-7b83-8d6d-7d1c61b3e9f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable_019fdc15-c471-7643-b244-b283d11e80be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossLineItems_019fdc15-c471-7b83-8d6d-7d1c61b3e9f3" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable_019fdc15-c471-7643-b244-b283d11e80be" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-78de-91d4-86cfec19d7a0" 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_DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable_019fdc15-c471-7643-b244-b283d11e80be" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-78de-91d4-86cfec19d7a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-78de-91d4-86cfec19d7a0_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_019fdc15-c471-78de-91d4-86cfec19d7a0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-78de-91d4-86cfec19d7a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7d42-9364-8e87fb948bdd" 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_019fdc15-c471-78de-91d4-86cfec19d7a0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7d42-9364-8e87fb948bdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_StructuredSecuritiesMember_019fdc15-c471-7a09-81ab-03f6fa92934f" xlink:href="afg-20260930.xsd#afg_StructuredSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7d42-9364-8e87fb948bdd" xlink:to="loc_afg_StructuredSecuritiesMember_019fdc15-c471-7a09-81ab-03f6fa92934f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c471-7496-a3eb-480e85c7ac18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7d42-9364-8e87fb948bdd" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019fdc15-c471-7496-a3eb-480e85c7ac18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019fdc15-c471-7b24-897e-80358beaffc7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableforsaleAllowanceForCreditLossLineItems_019fdc15-c471-7b83-8d6d-7d1c61b3e9f3" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019fdc15-c471-7b24-897e-80358beaffc7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019fdc15-c471-7b0b-b44d-4f23a4ed10f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019fdc15-c471-7b24-897e-80358beaffc7" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019fdc15-c471-7b0b-b44d-4f23a4ed10f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_019fdc15-c471-7c6c-84a5-5df9232031b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019fdc15-c471-7b24-897e-80358beaffc7" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_019fdc15-c471-7c6c-84a5-5df9232031b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal_019fdc15-c471-7040-9e86-5c5d5d5b0744" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019fdc15-c471-7b24-897e-80358beaffc7" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal_019fdc15-c471-7040-9e86-5c5d5d5b0744" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossSecuritiesSold_019fdc15-c471-7a20-b224-2685b3213970" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossSecuritiesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossRollForward_019fdc15-c471-7b24-897e-80358beaffc7" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossSecuritiesSold_019fdc15-c471-7a20-b224-2685b3213970" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_019fdc15-c471-78a9-8298-7fd9facf158b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsScheduledmaturitiesofavailableforsalefixedmaturitiesDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsScheduledmaturitiesofavailableforsalefixedmaturitiesDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsScheduledmaturitiesofavailableforsalefixedmaturitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7178-acfa-de7dd1a6bada" 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_019fdc15-c471-79e0-b071-959f68366245" 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_019fdc15-c471-7178-acfa-de7dd1a6bada" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fdc15-c471-79e0-b071-959f68366245" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7fc7-ad9a-004fb64051f4" 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_019fdc15-c471-79e0-b071-959f68366245" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7fc7-ad9a-004fb64051f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7fc7-ad9a-004fb64051f4_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_019fdc15-c471-7fc7-ad9a-004fb64051f4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7fc7-ad9a-004fb64051f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-77f9-8bbc-11e3a8b33d32" 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_019fdc15-c471-7fc7-ad9a-004fb64051f4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-77f9-8bbc-11e3a8b33d32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7424-9b8c-e46340adddc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-77f9-8bbc-11e3a8b33d32" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7424-9b8c-e46340adddc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_CollateralizedLoanObligationsAndOtherAssetBackedSecuritiesMember_019fdc15-c471-760c-bfde-41a35a8f4982" xlink:href="afg-20260930.xsd#afg_CollateralizedLoanObligationsAndOtherAssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-77f9-8bbc-11e3a8b33d32" xlink:to="loc_afg_CollateralizedLoanObligationsAndOtherAssetBackedSecuritiesMember_019fdc15-c471-760c-bfde-41a35a8f4982" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_019fdc15-c471-7b5d-807f-ad1c31397187" 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_019fdc15-c471-77f9-8bbc-11e3a8b33d32" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_019fdc15-c471-7b5d-807f-ad1c31397187" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_019fdc15-c471-7903-b91b-7e2461f7761e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7178-acfa-de7dd1a6bada" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_019fdc15-c471-7903-b91b-7e2461f7761e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_019fdc15-c471-7903-b91b-7e2461f7761e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_019fdc15-c471-7863-b0c6-e7777412b9f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_019fdc15-c471-7863-b0c6-e7777412b9f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_019fdc15-c471-7239-8463-c14ab75ed945" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_019fdc15-c471-7239-8463-c14ab75ed945" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_019fdc15-c471-7768-876a-49f0bade445c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_019fdc15-c471-7768-876a-49f0bade445c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost_019fdc15-c471-74cd-8454-158e66a0dc27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost_019fdc15-c471-74cd-8454-158e66a0dc27" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsAmortizedCost_019fdc15-c471-78bb-b9a2-0242de8a1888" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsAmortizedCost_019fdc15-c471-78bb-b9a2-0242de8a1888" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost_019fdc15-c471-7eab-8b8f-c981a0de56e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost_019fdc15-c471-7eab-8b8f-c981a0de56e6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAfterAllowanceForCreditLoss_019fdc15-c471-71aa-838d-664c1788468c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract_019fdc15-c471-7860-ade0-89efd2bd7a85" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAfterAllowanceForCreditLoss_019fdc15-c471-71aa-838d-664c1788468c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_019fdc15-c471-7903-b91b-7e2461f7761e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_019fdc15-c471-72d4-971a-469794c56c42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_019fdc15-c471-72d4-971a-469794c56c42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_019fdc15-c471-7bcc-a694-98096bbcce7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_019fdc15-c471-7bcc-a694-98096bbcce7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_019fdc15-c471-7598-91c4-b56e59eafce7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_019fdc15-c471-7598-91c4-b56e59eafce7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_019fdc15-c471-7b0a-86da-01ab00f0cfd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_019fdc15-c471-7b0a-86da-01ab00f0cfd5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsFairValue_019fdc15-c471-7af0-9e9b-24f8757c5c88" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsFairValue_019fdc15-c471-7af0-9e9b-24f8757c5c88" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue_019fdc15-c471-7ff8-acc0-cf90fb7e761e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue_019fdc15-c471-7ff8-acc0-cf90fb7e761e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c471-7f15-8c5b-d305d66c1f40" 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_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract_019fdc15-c471-70a1-a8b6-df590ec4e983" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c471-7f15-8c5b-d305d66c1f40" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_019fdc15-c471-7903-b91b-7e2461f7761e" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValuePercent_019fdc15-c471-7939-b5fd-d45d31e66199" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValuePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValuePercent_019fdc15-c471-7939-b5fd-d45d31e66199" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValuePercent_019fdc15-c471-79cd-8f56-79e172ebefb2" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValuePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValuePercent_019fdc15-c471-79cd-8f56-79e172ebefb2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValuePercent_019fdc15-c471-7b80-883a-fe1f89c1f6bd" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValuePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValuePercent_019fdc15-c471-7b80-883a-fe1f89c1f6bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValuePercent_019fdc15-c471-706b-9fd1-2f76ab478e2c" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValuePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValuePercent_019fdc15-c471-706b-9fd1-2f76ab478e2c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsFairValuePercent_019fdc15-c471-752d-bbde-558e89a8d4f1" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsFairValuePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesExcludingAbsAndMbsFairValuePercent_019fdc15-c471-752d-bbde-558e89a8d4f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValuePercent_019fdc15-c471-7329-a25a-53665b00618c" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValuePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValuePercent_019fdc15-c471-7329-a25a-53665b00618c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercent_019fdc15-c471-771f-bed1-b9773eb4993d" xlink:href="afg-20260930.xsd#afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercentFiscalYearMaturityAbstract_019fdc15-c471-741e-9bac-45cf54fd147b" xlink:to="loc_afg_AvailableForSaleSecuritiesDebtMaturitiesFairValuePercent_019fdc15-c471-771f-bed1-b9773eb4993d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_CollateralizedLoanObligationsandOtherAssetBackedSecuritiesAverageUsefulLife_019fdc15-c471-777d-9794-06021a1c0c67" xlink:href="afg-20260930.xsd#afg_CollateralizedLoanObligationsandOtherAssetBackedSecuritiesAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_019fdc15-c471-7903-b91b-7e2461f7761e" xlink:to="loc_afg_CollateralizedLoanObligationsandOtherAssetBackedSecuritiesAverageUsefulLife_019fdc15-c471-777d-9794-06021a1c0c67" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_MortgageBackedSecuritiesAverageUsefulLife_019fdc15-c471-72ff-9a88-60cc99a1de92" xlink:href="afg-20260930.xsd#afg_MortgageBackedSecuritiesAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAbstract_019fdc15-c471-7903-b91b-7e2461f7761e" xlink:to="loc_afg_MortgageBackedSecuritiesAverageUsefulLife_019fdc15-c471-72ff-9a88-60cc99a1de92" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsScheduleofsourcesofnetinvestmentincomeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsScheduleofsourcesofnetinvestmentincomeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsScheduleofsourcesofnetinvestmentincomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fdc15-c471-794c-b16c-1edcf96da872" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fdc15-c471-794c-b16c-1edcf96da872" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019fdc15-c471-7e2d-a8a6-4ef455a75414" 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_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fdc15-c471-794c-b16c-1edcf96da872" xlink:to="loc_us-gaap_InvestmentTypeAxis_019fdc15-c471-7e2d-a8a6-4ef455a75414" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7e2d-a8a6-4ef455a75414_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_019fdc15-c471-7e2d-a8a6-4ef455a75414" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7e2d-a8a6-4ef455a75414_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" 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_019fdc15-c471-7e2d-a8a6-4ef455a75414" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-79f8-a674-e34134c33d7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-79f8-a674-e34134c33d7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-7847-b72e-2e496b91ce8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-7847-b72e-2e496b91ce8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_019fdc15-c471-77fb-873d-83b450e0e1ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_019fdc15-c471-77fb-873d-83b450e0e1ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesMember_019fdc15-c471-707c-8ba9-b5623e66f84d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgagesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_MortgagesMember_019fdc15-c471-707c-8ba9-b5623e66f84d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_CharlestonHarborResortMarinaMember_01a18916-0753-79d3-b0c4-c8cc29680755" xlink:href="afg-20260930.xsd#afg_CharlestonHarborResortMarinaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_afg_CharlestonHarborResortMarinaMember_01a18916-0753-79d3-b0c4-c8cc29680755" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_019fdc15-c471-7876-846d-9a8ccc7a1cf5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLongTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_019fdc15-c471-7876-846d-9a8ccc7a1cf5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fdc15-c471-702a-919e-de699226199f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fdc15-c471-794c-b16c-1edcf96da872" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fdc15-c471-702a-919e-de699226199f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_GrossInvestmentIncomeOperatingInterestAndAmortization_019fdc15-c471-729e-95cd-389e763e2d32" xlink:href="afg-20260930.xsd#afg_GrossInvestmentIncomeOperatingInterestAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_afg_GrossInvestmentIncomeOperatingInterestAndAmortization_019fdc15-c471-729e-95cd-389e763e2d32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DebtSecuritiesTradingAndConvertibleChangeInFairValue_019fdc15-c471-796b-ba2d-a954587f6ecd" xlink:href="afg-20260930.xsd#afg_DebtSecuritiesTradingAndConvertibleChangeInFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_afg_DebtSecuritiesTradingAndConvertibleChangeInFairValue_019fdc15-c471-796b-ba2d-a954587f6ecd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeDividend_019fdc15-c471-7fa9-9113-e0fec4a9495b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeDividend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_InvestmentIncomeDividend_019fdc15-c471-7fa9-9113-e0fec4a9495b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiGainLoss_019fdc15-c471-73f5-9b5e-8ab193e6b7e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNiGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_EquitySecuritiesFvNiGainLoss_019fdc15-c471-73f5-9b5e-8ab193e6b7e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019fdc15-c471-7b84-b978-749351015ed8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019fdc15-c471-7b84-b978-749351015ed8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_019fdc15-c471-7a12-b3c2-c69741f6b3cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_019fdc15-c471-7a12-b3c2-c69741f6b3cc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInvestmentExpense_019fdc15-c471-7d61-af0e-9c625dcdf5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInvestmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_InvestmentIncomeInvestmentExpense_019fdc15-c471-7d61-af0e-9c625dcdf5c2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019fdc15-c471-7ba9-b0c4-ca2395c5ccbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_NetInvestmentIncome_019fdc15-c471-7ba9-b0c4-ca2395c5ccbb" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsScheduleofsourcesofnetinvestmentincomeDetails_1" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsScheduleofsourcesofnetinvestmentincomeDetails_1"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsScheduleofsourcesofnetinvestmentincomeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fdc15-c471-794c-b16c-1edcf96da872" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fdc15-c471-794c-b16c-1edcf96da872" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019fdc15-c471-7e2d-a8a6-4ef455a75414" 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_ScheduleOfInvestmentIncomeReportedAmountsByCategoryTable_019fdc15-c471-794c-b16c-1edcf96da872" xlink:to="loc_us-gaap_InvestmentTypeAxis_019fdc15-c471-7e2d-a8a6-4ef455a75414" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7e2d-a8a6-4ef455a75414_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_019fdc15-c471-7e2d-a8a6-4ef455a75414" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7e2d-a8a6-4ef455a75414_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" 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_019fdc15-c471-7e2d-a8a6-4ef455a75414" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-79f8-a674-e34134c33d7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-79f8-a674-e34134c33d7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-7847-b72e-2e496b91ce8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-7847-b72e-2e496b91ce8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_019fdc15-c471-77fb-873d-83b450e0e1ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_019fdc15-c471-77fb-873d-83b450e0e1ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesMember_019fdc15-c471-707c-8ba9-b5623e66f84d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MortgagesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_MortgagesMember_019fdc15-c471-707c-8ba9-b5623e66f84d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_CharlestonHarborResortMarinaMember_01a18916-0753-79d3-b0c4-c8cc29680755" xlink:href="afg-20260930.xsd#afg_CharlestonHarborResortMarinaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_afg_CharlestonHarborResortMarinaMember_01a18916-0753-79d3-b0c4-c8cc29680755" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_019fdc15-c471-7876-846d-9a8ccc7a1cf5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLongTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019fdc15-c471-7055-9bf2-76fbef3b80a9" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_019fdc15-c471-7876-846d-9a8ccc7a1cf5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_GrossInvestmentIncomeOperatingInterestAndAmortization_019fdc15-c471-729e-95cd-389e763e2d32" xlink:href="afg-20260930.xsd#afg_GrossInvestmentIncomeOperatingInterestAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_afg_GrossInvestmentIncomeOperatingInterestAndAmortization_019fdc15-c471-729e-95cd-389e763e2d32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DebtSecuritiesTradingAndConvertibleChangeInFairValue_019fdc15-c471-796b-ba2d-a954587f6ecd" xlink:href="afg-20260930.xsd#afg_DebtSecuritiesTradingAndConvertibleChangeInFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_afg_DebtSecuritiesTradingAndConvertibleChangeInFairValue_019fdc15-c471-796b-ba2d-a954587f6ecd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeDividend_019fdc15-c471-7fa9-9113-e0fec4a9495b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeDividend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_InvestmentIncomeDividend_019fdc15-c471-7fa9-9113-e0fec4a9495b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiGainLoss_019fdc15-c471-73f5-9b5e-8ab193e6b7e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesFvNiGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_EquitySecuritiesFvNiGainLoss_019fdc15-c471-73f5-9b5e-8ab193e6b7e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019fdc15-c471-7b84-b978-749351015ed8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019fdc15-c471-7b84-b978-749351015ed8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_019fdc15-c471-7a12-b3c2-c69741f6b3cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_019fdc15-c471-7a12-b3c2-c69741f6b3cc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInvestmentExpense_019fdc15-c471-7d61-af0e-9c625dcdf5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInvestmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_InvestmentIncomeInvestmentExpense_019fdc15-c471-7d61-af0e-9c625dcdf5c2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_019fdc15-c471-7ba9-b0c4-ca2395c5ccbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_019fdc15-c471-7016-a289-bacc0f308a30" xlink:to="loc_us-gaap_NetInvestmentIncome_019fdc15-c471-7ba9-b0c4-ca2395c5ccbb" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsRealizedgainslossesandchangesinunrealizedappreciationdepreciationrelatedtofixedmaturityandequitysecurityinvestmentsDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsRealizedgainslossesandchangesinunrealizedappreciationdepreciationrelatedtofixedmaturityandequitysecurityinvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsRealizedgainslossesandchangesinunrealizedappreciationdepreciationrelatedtofixedmaturityandequitysecurityinvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7207-986a-8c1ceb56ef8e" 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_019fdc15-c471-7e1f-8cb3-5d8dd6b005df" 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_019fdc15-c471-7207-986a-8c1ceb56ef8e" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fdc15-c471-7e1f-8cb3-5d8dd6b005df" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7680-806e-63ace664dbe4" 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_019fdc15-c471-7e1f-8cb3-5d8dd6b005df" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7680-806e-63ace664dbe4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7680-806e-63ace664dbe4_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_019fdc15-c471-7680-806e-63ace664dbe4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7680-806e-63ace664dbe4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7ab1-a999-b88741e102f9" 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_019fdc15-c471-7680-806e-63ace664dbe4" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7ab1-a999-b88741e102f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NetOfTaxMember_019fdc15-c471-7f40-b304-5adabca8a5f1" xlink:href="afg-20260930.xsd#afg_NetOfTaxMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7ab1-a999-b88741e102f9" xlink:to="loc_afg_NetOfTaxMember_019fdc15-c471-7f40-b304-5adabca8a5f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PretaxMember_019fdc15-c471-7f88-847e-2120f9a855ad" xlink:href="afg-20260930.xsd#afg_PretaxMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_NetOfTaxMember_019fdc15-c471-7f40-b304-5adabca8a5f1" xlink:to="loc_afg_PretaxMember_019fdc15-c471-7f88-847e-2120f9a855ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-76ad-8221-357408a23c4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_PretaxMember_019fdc15-c471-7f88-847e-2120f9a855ad" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-76ad-8221-357408a23c4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-7fdc-89ad-519bec8fdd12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_PretaxMember_019fdc15-c471-7f88-847e-2120f9a855ad" xlink:to="loc_us-gaap_EquitySecuritiesMember_019fdc15-c471-7fdc-89ad-519bec8fdd12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_MortgageLoansAndOtherInvestmentsMember_019fdc15-c471-73fc-ac4b-5c2e0d234ef3" xlink:href="afg-20260930.xsd#afg_MortgageLoansAndOtherInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_PretaxMember_019fdc15-c471-7f88-847e-2120f9a855ad" xlink:to="loc_afg_MortgageLoansAndOtherInvestmentsMember_019fdc15-c471-73fc-ac4b-5c2e0d234ef3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_TaxEffectsMember_019fdc15-c471-7ffb-a870-4c13b6b67a04" xlink:href="afg-20260930.xsd#afg_TaxEffectsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7ab1-a999-b88741e102f9" xlink:to="loc_afg_TaxEffectsMember_019fdc15-c471-7ffb-a870-4c13b6b67a04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract_019fdc15-c471-7a92-bb82-819ffbf85c86" xlink:href="afg-20260930.xsd#afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7207-986a-8c1ceb56ef8e" xlink:to="loc_afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract_019fdc15-c471-7a92-bb82-819ffbf85c86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments_019fdc15-c471-79c5-b744-4ddbb79e6f11" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract_019fdc15-c471-7a92-bb82-819ffbf85c86" xlink:to="loc_us-gaap_MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments_019fdc15-c471-79c5-b744-4ddbb79e6f11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossPeriodIncreaseDecrease_019fdc15-c471-7009-b26e-7137d5505acd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract_019fdc15-c471-7a92-bb82-819ffbf85c86" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossPeriodIncreaseDecrease_019fdc15-c471-7009-b26e-7137d5505acd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease_019fdc15-c471-7d0b-b2f2-1b9ca4a7da06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract_019fdc15-c471-7a92-bb82-819ffbf85c86" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease_019fdc15-c471-7d0b-b2f2-1b9ca4a7da06" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_InvestmentsAllowanceForCreditLossPeriodIncreaseDecrease_019fdc15-c471-7b15-bde3-c79732e7383b" xlink:href="afg-20260930.xsd#afg_InvestmentsAllowanceForCreditLossPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract_019fdc15-c471-7a92-bb82-819ffbf85c86" xlink:to="loc_afg_InvestmentsAllowanceForCreditLossPeriodIncreaseDecrease_019fdc15-c471-7b15-bde3-c79732e7383b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_019fdc15-c471-7a72-9370-cf319def3944" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtAndEquitySecuritiesRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract_019fdc15-c471-7a92-bb82-819ffbf85c86" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_019fdc15-c471-7a72-9370-cf319def3944" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_ChangeInUnrealizedAppreciationDepreciation_019fdc15-c471-72c4-87a0-106506499899" xlink:href="afg-20260930.xsd#afg_ChangeInUnrealizedAppreciationDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_RealizedGainsLossesAndChangesInUnrealizedAppreciationDepreciationRelatedToFixedMaturityAndEquitySecurityInvestmentsAbstract_019fdc15-c471-7a92-bb82-819ffbf85c86" xlink:to="loc_afg_ChangeInUnrealizedAppreciationDepreciation_019fdc15-c471-72c4-87a0-106506499899" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsHoldinggainslossesonequitysecuritiesstillheldDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsHoldinggainslossesonequitysecuritiesstillheldDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsHoldinggainslossesonequitysecuritiesstillheldDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldLineItems_019fdc15-c471-7c83-9eb0-ef1617e1bb20" xlink:href="afg-20260930.xsd#afg_HoldingGainsLossesonEquitySecuritiesStillHeldLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldTable_019fdc15-c471-7f50-a410-154cc121fdda" xlink:href="afg-20260930.xsd#afg_HoldingGainsLossesonEquitySecuritiesStillHeldTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldLineItems_019fdc15-c471-7c83-9eb0-ef1617e1bb20" xlink:to="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldTable_019fdc15-c471-7f50-a410-154cc121fdda" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fdc15-c471-7d78-b9ea-1b897b9d94cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldTable_019fdc15-c471-7f50-a410-154cc121fdda" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fdc15-c471-7d78-b9ea-1b897b9d94cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_019fdc15-c471-7c36-b2b9-2ea60bfd4dcb" 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_afg_HoldingGainsLossesonEquitySecuritiesStillHeldLineItems_019fdc15-c471-7c83-9eb0-ef1617e1bb20" xlink:to="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_019fdc15-c471-7c36-b2b9-2ea60bfd4dcb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsHoldinggainslossesonequitysecuritiesstillheldDetails_1" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsHoldinggainslossesonequitysecuritiesstillheldDetails_1"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsHoldinggainslossesonequitysecuritiesstillheldDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldLineItems_019fdc15-c471-7c83-9eb0-ef1617e1bb20" xlink:href="afg-20260930.xsd#afg_HoldingGainsLossesonEquitySecuritiesStillHeldLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldTable_019fdc15-c471-7f50-a410-154cc121fdda" xlink:href="afg-20260930.xsd#afg_HoldingGainsLossesonEquitySecuritiesStillHeldTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldLineItems_019fdc15-c471-7c83-9eb0-ef1617e1bb20" xlink:to="loc_afg_HoldingGainsLossesonEquitySecuritiesStillHeldTable_019fdc15-c471-7f50-a410-154cc121fdda" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_019fdc15-c471-7c36-b2b9-2ea60bfd4dcb" 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_afg_HoldingGainsLossesonEquitySecuritiesStillHeldLineItems_019fdc15-c471-7c83-9eb0-ef1617e1bb20" xlink:to="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_019fdc15-c471-7c36-b2b9-2ea60bfd4dcb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/InvestmentsGrossrealizedgainsandlossesonavailableforsalefixedmaturityinvestmenttransactionsDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#InvestmentsGrossrealizedgainsandlossesonavailableforsalefixedmaturityinvestmenttransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/InvestmentsGrossrealizedgainsandlossesonavailableforsalefixedmaturityinvestmenttransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7ff4-9356-5208506408af" 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_019fdc15-c471-73d2-b46c-acc6002a001b" 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_019fdc15-c471-7ff4-9356-5208506408af" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_019fdc15-c471-73d2-b46c-acc6002a001b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-74bc-ac39-73209690ee91" 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_019fdc15-c471-73d2-b46c-acc6002a001b" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-74bc-ac39-73209690ee91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-74bc-ac39-73209690ee91_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_019fdc15-c471-74bc-ac39-73209690ee91" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-74bc-ac39-73209690ee91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-795b-a124-cac6dee2b348" 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_019fdc15-c471-74bc-ac39-73209690ee91" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-795b-a124-cac6dee2b348" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7332-9db7-1bf69f02c884" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FixedMaturitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-795b-a124-cac6dee2b348" xlink:to="loc_us-gaap_FixedMaturitiesMember_019fdc15-c471-7332-9db7-1bf69f02c884" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract_019fdc15-c471-7a24-ba06-63024b2ac29c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019fdc15-c471-7ff4-9356-5208506408af" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract_019fdc15-c471-7a24-ba06-63024b2ac29c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedGain_019fdc15-c471-7cf2-a802-c2d52ff424fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract_019fdc15-c471-7a24-ba06-63024b2ac29c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedGain_019fdc15-c471-7cf2-a802-c2d52ff424fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss_019fdc15-c471-78cf-a022-11236d161321" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract_019fdc15-c471-7a24-ba06-63024b2ac29c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss_019fdc15-c471-78cf-a022-11236d161321" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/DerivativesDerivativesincludedintheBalanceSheetatfairvalueDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#DerivativesDerivativesincludedintheBalanceSheetatfairvalueDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/DerivativesDerivativesincludedintheBalanceSheetatfairvalueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativesFairValueLineItems_019fdc15-c471-708a-af37-c88fdd980387" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativesFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019fdc15-c471-76a0-a2a1-51c56ac439d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019fdc15-c471-708a-af37-c88fdd980387" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019fdc15-c471-76a0-a2a1-51c56ac439d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7fbf-b4cf-101603180db7" 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_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019fdc15-c471-76a0-a2a1-51c56ac439d1" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7fbf-b4cf-101603180db7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7fbf-b4cf-101603180db7_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_019fdc15-c471-7fbf-b4cf-101603180db7" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7fbf-b4cf-101603180db7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7172-88eb-5f245adb02a3" 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_019fdc15-c471-7fbf-b4cf-101603180db7" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7172-88eb-5f245adb02a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-75b6-98a3-424ecd08a53b" 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_019fdc15-c471-7172-88eb-5f245adb02a3" xlink:to="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-75b6-98a3-424ecd08a53b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember_019fdc15-c471-7c18-8990-06ac7f384980" xlink:href="afg-20260930.xsd#afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7172-88eb-5f245adb02a3" xlink:to="loc_afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember_019fdc15-c471-7c18-8990-06ac7f384980" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-77aa-924f-367224bc1835" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7172-88eb-5f245adb02a3" xlink:to="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-77aa-924f-367224bc1835" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-7a2c-bf56-e1f176cd198d" 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_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019fdc15-c471-76a0-a2a1-51c56ac439d1" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-7a2c-bf56-e1f176cd198d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7a2c-bf56-e1f176cd198d_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_019fdc15-c471-7a2c-bf56-e1f176cd198d" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7a2c-bf56-e1f176cd198d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7303-a31d-0b6405fbebb3" 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_019fdc15-c471-7a2c-bf56-e1f176cd198d" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7303-a31d-0b6405fbebb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-7e5a-8e51-1a2d3a3320a3" 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_019fdc15-c471-7303-a31d-0b6405fbebb3" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-7e5a-8e51-1a2d3a3320a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019fdc15-c471-795f-ab27-d6dafe4b970b" 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_019fdc15-c471-7303-a31d-0b6405fbebb3" xlink:to="loc_us-gaap_NondesignatedMember_019fdc15-c471-795f-ab27-d6dafe4b970b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019fdc15-c471-7959-b58a-4197311071dc" 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_DerivativesFairValueLineItems_019fdc15-c471-708a-af37-c88fdd980387" xlink:to="loc_us-gaap_DerivativeAssets_019fdc15-c471-7959-b58a-4197311071dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019fdc15-c471-7367-98cf-4d24ff8954a3" 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_DerivativesFairValueLineItems_019fdc15-c471-708a-af37-c88fdd980387" xlink:to="loc_us-gaap_DerivativeLiabilities_019fdc15-c471-7367-98cf-4d24ff8954a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration_019fdc15-c471-79d5-98ab-d92a10436b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019fdc15-c471-708a-af37-c88fdd980387" xlink:to="loc_us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration_019fdc15-c471-79d5-98ab-d92a10436b7c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration_019fdc15-c471-7bc6-8dfa-157839947476" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019fdc15-c471-708a-af37-c88fdd980387" xlink:to="loc_us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration_019fdc15-c471-7bc6-8dfa-157839947476" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/DerivativesNarrativeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#DerivativesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/DerivativesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7431-957d-3a21e012bfcd" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7431-957d-3a21e012bfcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7431-957d-3a21e012bfcd_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_019fdc15-c471-7431-957d-3a21e012bfcd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7431-957d-3a21e012bfcd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7c28-b8e2-2c847d52a606" 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_019fdc15-c471-7431-957d-3a21e012bfcd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7c28-b8e2-2c847d52a606" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-7d2c-b176-7c4022ea79a7" 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_019fdc15-c471-7c28-b8e2-2c847d52a606" xlink:to="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-7d2c-b176-7c4022ea79a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NewInterestRateSwapsEnteredDuringPeriodMember_019fdc15-c471-7d18-805b-6952cae2e182" xlink:href="afg-20260930.xsd#afg_NewInterestRateSwapsEnteredDuringPeriodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7c28-b8e2-2c847d52a606" xlink:to="loc_afg_NewInterestRateSwapsEnteredDuringPeriodMember_019fdc15-c471-7d18-805b-6952cae2e182" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-7605-9481-f50734f57671" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7c28-b8e2-2c847d52a606" xlink:to="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-7605-9481-f50734f57671" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fdc15-c471-7f1a-8ca4-8749e0fbb191" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fdc15-c471-7f1a-8ca4-8749e0fbb191" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fdc15-c471-7f1a-8ca4-8749e0fbb191_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_019fdc15-c471-7f1a-8ca4-8749e0fbb191" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fdc15-c471-7f1a-8ca4-8749e0fbb191_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fdc15-c471-71b7-838d-7402ac4acf0c" 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_019fdc15-c471-7f1a-8ca4-8749e0fbb191" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fdc15-c471-71b7-838d-7402ac4acf0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019fdc15-c471-724a-95c8-fd45b51bd7ce" 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_019fdc15-c471-71b7-838d-7402ac4acf0c" xlink:to="loc_us-gaap_CashFlowHedgingMember_019fdc15-c471-724a-95c8-fd45b51bd7ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-713b-b288-52beb813353b" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-713b-b288-52beb813353b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-713b-b288-52beb813353b_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_019fdc15-c471-713b-b288-52beb813353b" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-713b-b288-52beb813353b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7b1b-8a42-845c529e0662" 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_019fdc15-c471-713b-b288-52beb813353b" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7b1b-8a42-845c529e0662" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-7182-ba4f-6221e4a1705f" 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_019fdc15-c471-7b1b-8a42-845c529e0662" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-7182-ba4f-6221e4a1705f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019fdc15-c471-70b8-8562-99831530565c" 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_019fdc15-c471-7b1b-8a42-845c529e0662" xlink:to="loc_us-gaap_NondesignatedMember_019fdc15-c471-70b8-8562-99831530565c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fdc15-c471-73fb-afc6-9de66456a3b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fdc15-c471-73fb-afc6-9de66456a3b5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fdc15-c471-7ad2-b4b2-27402031b2f4" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_srt_RangeAxis_019fdc15-c471-7ad2-b4b2-27402031b2f4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fdc15-c471-7ad2-b4b2-27402031b2f4_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_019fdc15-c471-7ad2-b4b2-27402031b2f4" xlink:to="loc_srt_RangeMember_019fdc15-c471-7ad2-b4b2-27402031b2f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fdc15-c471-7593-a66e-57f41b0e3db2" 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_019fdc15-c471-7ad2-b4b2-27402031b2f4" xlink:to="loc_srt_RangeMember_019fdc15-c471-7593-a66e-57f41b0e3db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fdc15-c471-7143-84d5-65d4186fa80e" 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_019fdc15-c471-7593-a66e-57f41b0e3db2" xlink:to="loc_srt_MaximumMember_019fdc15-c471-7143-84d5-65d4186fa80e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019fdc15-c471-7faa-a188-192a0b20b147" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019fdc15-c471-7faa-a188-192a0b20b147" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019fdc15-c471-733f-8890-f000e3bee315" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019fdc15-c471-733f-8890-f000e3bee315" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_019fdc15-c471-729c-834f-c2848bb6963d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_019fdc15-c471-729c-834f-c2848bb6963d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DerivativeLiabilityNotSubjectToMasterNettingArrangementCollateralRightToReclaimCash_019fdc15-c471-7ec5-9863-de0f976fdba7" xlink:href="afg-20260930.xsd#afg_DerivativeLiabilityNotSubjectToMasterNettingArrangementCollateralRightToReclaimCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_afg_DerivativeLiabilityNotSubjectToMasterNettingArrangementCollateralRightToReclaimCash_019fdc15-c471-7ec5-9863-de0f976fdba7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DerivativeAssetNotSubjectToMasterNettingArrangementCollateralObligationToReturnCash_019fdc15-c471-7e5c-8302-48d2ba2893fa" xlink:href="afg-20260930.xsd#afg_DerivativeAssetNotSubjectToMasterNettingArrangementCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_afg_DerivativeAssetNotSubjectToMasterNettingArrangementCollateralObligationToReturnCash_019fdc15-c471-7e5c-8302-48d2ba2893fa" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/DerivativesNarrativeDetails_1" xlink:type="simple" xlink:href="afg-20260930.xsd#DerivativesNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/DerivativesNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7431-957d-3a21e012bfcd" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7431-957d-3a21e012bfcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7431-957d-3a21e012bfcd_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_019fdc15-c471-7431-957d-3a21e012bfcd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7431-957d-3a21e012bfcd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7c28-b8e2-2c847d52a606" 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_019fdc15-c471-7431-957d-3a21e012bfcd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7c28-b8e2-2c847d52a606" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-7d2c-b176-7c4022ea79a7" 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_019fdc15-c471-7c28-b8e2-2c847d52a606" xlink:to="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-7d2c-b176-7c4022ea79a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NewInterestRateSwapsEnteredDuringPeriodMember_019fdc15-c471-7d18-805b-6952cae2e182" xlink:href="afg-20260930.xsd#afg_NewInterestRateSwapsEnteredDuringPeriodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7c28-b8e2-2c847d52a606" xlink:to="loc_afg_NewInterestRateSwapsEnteredDuringPeriodMember_019fdc15-c471-7d18-805b-6952cae2e182" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-7605-9481-f50734f57671" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7c28-b8e2-2c847d52a606" xlink:to="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-7605-9481-f50734f57671" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fdc15-c471-7f1a-8ca4-8749e0fbb191" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019fdc15-c471-7f1a-8ca4-8749e0fbb191" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fdc15-c471-7f1a-8ca4-8749e0fbb191_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_019fdc15-c471-7f1a-8ca4-8749e0fbb191" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fdc15-c471-7f1a-8ca4-8749e0fbb191_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019fdc15-c471-71b7-838d-7402ac4acf0c" 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_019fdc15-c471-7f1a-8ca4-8749e0fbb191" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019fdc15-c471-71b7-838d-7402ac4acf0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019fdc15-c471-724a-95c8-fd45b51bd7ce" 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_019fdc15-c471-71b7-838d-7402ac4acf0c" xlink:to="loc_us-gaap_CashFlowHedgingMember_019fdc15-c471-724a-95c8-fd45b51bd7ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-713b-b288-52beb813353b" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-713b-b288-52beb813353b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-713b-b288-52beb813353b_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_019fdc15-c471-713b-b288-52beb813353b" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-713b-b288-52beb813353b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7b1b-8a42-845c529e0662" 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_019fdc15-c471-713b-b288-52beb813353b" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7b1b-8a42-845c529e0662" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-7182-ba4f-6221e4a1705f" 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_019fdc15-c471-7b1b-8a42-845c529e0662" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-7182-ba4f-6221e4a1705f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019fdc15-c471-70b8-8562-99831530565c" 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_019fdc15-c471-7b1b-8a42-845c529e0662" xlink:to="loc_us-gaap_NondesignatedMember_019fdc15-c471-70b8-8562-99831530565c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fdc15-c471-7ad2-b4b2-27402031b2f4" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7a85-b6f2-9d10f7c43e0f" xlink:to="loc_srt_RangeAxis_019fdc15-c471-7ad2-b4b2-27402031b2f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fdc15-c471-7ad2-b4b2-27402031b2f4_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_019fdc15-c471-7ad2-b4b2-27402031b2f4" xlink:to="loc_srt_RangeMember_019fdc15-c471-7ad2-b4b2-27402031b2f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fdc15-c471-7593-a66e-57f41b0e3db2" 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_019fdc15-c471-7ad2-b4b2-27402031b2f4" xlink:to="loc_srt_RangeMember_019fdc15-c471-7593-a66e-57f41b0e3db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fdc15-c471-7143-84d5-65d4186fa80e" 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_019fdc15-c471-7593-a66e-57f41b0e3db2" xlink:to="loc_srt_MaximumMember_019fdc15-c471-7143-84d5-65d4186fa80e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019fdc15-c471-7faa-a188-192a0b20b147" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019fdc15-c471-7faa-a188-192a0b20b147" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019fdc15-c471-733f-8890-f000e3bee315" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019fdc15-c471-733f-8890-f000e3bee315" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_019fdc15-c471-729c-834f-c2848bb6963d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_019fdc15-c471-729c-834f-c2848bb6963d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DerivativeLiabilityNotSubjectToMasterNettingArrangementCollateralRightToReclaimCash_019fdc15-c471-7ec5-9863-de0f976fdba7" xlink:href="afg-20260930.xsd#afg_DerivativeLiabilityNotSubjectToMasterNettingArrangementCollateralRightToReclaimCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_afg_DerivativeLiabilityNotSubjectToMasterNettingArrangementCollateralRightToReclaimCash_019fdc15-c471-7ec5-9863-de0f976fdba7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DerivativeAssetNotSubjectToMasterNettingArrangementCollateralObligationToReturnCash_019fdc15-c471-7e5c-8302-48d2ba2893fa" xlink:href="afg-20260930.xsd#afg_DerivativeAssetNotSubjectToMasterNettingArrangementCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-72a5-8041-59e732f0e159" xlink:to="loc_afg_DerivativeAssetNotSubjectToMasterNettingArrangementCollateralObligationToReturnCash_019fdc15-c471-7e5c-8302-48d2ba2893fa" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/DerivativesGainslossesincludedintheStatementofEarningsforchangesinthefairvalueofderivativesDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#DerivativesGainslossesincludedintheStatementofEarningsforchangesinthefairvalueofderivativesDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/DerivativesGainslossesincludedintheStatementofEarningsforchangesinthefairvalueofderivativesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-77ee-93d4-d2ef092339ab" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-77ee-93d4-d2ef092339ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-77ee-93d4-d2ef092339ab_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_019fdc15-c471-77ee-93d4-d2ef092339ab" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-77ee-93d4-d2ef092339ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7acf-8882-73399a222d05" 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_019fdc15-c471-77ee-93d4-d2ef092339ab" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7acf-8882-73399a222d05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-731d-aeac-afcaa4b336df" 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_019fdc15-c471-7acf-8882-73399a222d05" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-731d-aeac-afcaa4b336df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7918-b27a-0cf5e7231eaf" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7918-b27a-0cf5e7231eaf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7918-b27a-0cf5e7231eaf_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_019fdc15-c471-7918-b27a-0cf5e7231eaf" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7918-b27a-0cf5e7231eaf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-78fd-ab28-158266513b77" 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_019fdc15-c471-7918-b27a-0cf5e7231eaf" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-78fd-ab28-158266513b77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-735d-a844-ab677189164c" 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_019fdc15-c471-78fd-ab28-158266513b77" xlink:to="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-735d-a844-ab677189164c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember_019fdc15-c471-7ed1-8461-75326a69fb42" xlink:href="afg-20260930.xsd#afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-78fd-ab28-158266513b77" xlink:to="loc_afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember_019fdc15-c471-7ed1-8461-75326a69fb42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-7208-9d2a-30f6ea99595e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-78fd-ab28-158266513b77" xlink:to="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-7208-9d2a-30f6ea99595e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fdc15-c471-72f2-a615-8f898fc60c15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019fdc15-c471-72f2-a615-8f898fc60c15" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019fdc15-c471-7a6a-a4f0-b9f07551c326" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019fdc15-c471-7a6a-a4f0-b9f07551c326" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_019fdc15-c471-7281-9042-f1a1b2f36a71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_019fdc15-c471-7281-9042-f1a1b2f36a71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_019fdc15-c471-764e-834d-5dac85d7059e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDerivativeInstrumentsNetPretax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:to="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_019fdc15-c471-764e-834d-5dac85d7059e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/DerivativesGainslossesincludedintheStatementofEarningsforchangesinthefairvalueofderivativesDetails_1" xlink:type="simple" xlink:href="afg-20260930.xsd#DerivativesGainslossesincludedintheStatementofEarningsforchangesinthefairvalueofderivativesDetails_1"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/DerivativesGainslossesincludedintheStatementofEarningsforchangesinthefairvalueofderivativesDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-77ee-93d4-d2ef092339ab" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:to="loc_us-gaap_HedgingDesignationAxis_019fdc15-c471-77ee-93d4-d2ef092339ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-77ee-93d4-d2ef092339ab_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_019fdc15-c471-77ee-93d4-d2ef092339ab" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-77ee-93d4-d2ef092339ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7acf-8882-73399a222d05" 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_019fdc15-c471-77ee-93d4-d2ef092339ab" xlink:to="loc_us-gaap_HedgingDesignationDomain_019fdc15-c471-7acf-8882-73399a222d05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-731d-aeac-afcaa4b336df" 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_019fdc15-c471-7acf-8882-73399a222d05" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019fdc15-c471-731d-aeac-afcaa4b336df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7918-b27a-0cf5e7231eaf" 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_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019fdc15-c471-7747-b9c0-e9e8bcd82dbe" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019fdc15-c471-7918-b27a-0cf5e7231eaf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7918-b27a-0cf5e7231eaf_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_019fdc15-c471-7918-b27a-0cf5e7231eaf" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-7918-b27a-0cf5e7231eaf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-78fd-ab28-158266513b77" 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_019fdc15-c471-7918-b27a-0cf5e7231eaf" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-78fd-ab28-158266513b77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-735d-a844-ab677189164c" 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_019fdc15-c471-78fd-ab28-158266513b77" xlink:to="loc_us-gaap_InterestRateSwapMember_019fdc15-c471-735d-a844-ab677189164c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember_019fdc15-c471-7ed1-8461-75326a69fb42" xlink:href="afg-20260930.xsd#afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-78fd-ab28-158266513b77" xlink:to="loc_afg_FixedMaturitySecuritiesWithEmbeddedDerivativesMember_019fdc15-c471-7ed1-8461-75326a69fb42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-7208-9d2a-30f6ea99595e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TotalReturnSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019fdc15-c471-78fd-ab28-158266513b77" xlink:to="loc_us-gaap_TotalReturnSwapMember_019fdc15-c471-7208-9d2a-30f6ea99595e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019fdc15-c471-7a6a-a4f0-b9f07551c326" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019fdc15-c471-7a6a-a4f0-b9f07551c326" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_019fdc15-c471-7281-9042-f1a1b2f36a71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_019fdc15-c471-7281-9042-f1a1b2f36a71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_019fdc15-c471-764e-834d-5dac85d7059e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDerivativeInstrumentsNetPretax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019fdc15-c471-7949-9fd6-272c1caf20b3" xlink:to="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_019fdc15-c471-764e-834d-5dac85d7059e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/ManagedInvestmentEntitiesNarrativeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#ManagedInvestmentEntitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/ManagedInvestmentEntitiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-7be8-b43b-ea8363fb7bda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-7be8-b43b-ea8363fb7bda" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-7c3b-91f3-54d906c6982e" 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_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-7be8-b43b-ea8363fb7bda" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-7c3b-91f3-54d906c6982e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7c3b-91f3-54d906c6982e_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_019fdc15-c471-7c3b-91f3-54d906c6982e" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7c3b-91f3-54d906c6982e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-71a8-b0f1-2cefabe9590a" 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_019fdc15-c471-7c3b-91f3-54d906c6982e" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-71a8-b0f1-2cefabe9590a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019fdc15-c471-703c-9138-af3a4fb89de4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-71a8-b0f1-2cefabe9590a" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019fdc15-c471-703c-9138-af3a4fb89de4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NewCollateralizedLoanObligationTemporaryWarehousingEntitiesMember_019fdc15-c471-7fa6-8c9f-5b637bf2eee6" xlink:href="afg-20260930.xsd#afg_NewCollateralizedLoanObligationTemporaryWarehousingEntitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-71a8-b0f1-2cefabe9590a" xlink:to="loc_afg_NewCollateralizedLoanObligationTemporaryWarehousingEntitiesMember_019fdc15-c471-7fa6-8c9f-5b637bf2eee6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NewCollateralizedLoanObligationEntitiesMember_019fdc15-c471-7599-8331-64125d93544d" xlink:href="afg-20260930.xsd#afg_NewCollateralizedLoanObligationEntitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-71a8-b0f1-2cefabe9590a" xlink:to="loc_afg_NewCollateralizedLoanObligationEntitiesMember_019fdc15-c471-7599-8331-64125d93544d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fdc15-c471-7c06-97c3-bfb25950bac5" 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_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-7be8-b43b-ea8363fb7bda" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fdc15-c471-7c06-97c3-bfb25950bac5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7c06-97c3-bfb25950bac5_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_019fdc15-c471-7c06-97c3-bfb25950bac5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7c06-97c3-bfb25950bac5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7962-bb0a-cd11d9f17ede" 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_019fdc15-c471-7c06-97c3-bfb25950bac5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7962-bb0a-cd11d9f17ede" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtObligationsMember_019fdc15-c471-7ddb-b8c6-65e130db7831" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubordinatedDebtObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7962-bb0a-cd11d9f17ede" xlink:to="loc_us-gaap_SubordinatedDebtObligationsMember_019fdc15-c471-7ddb-b8c6-65e130db7831" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_ManagedbyThirdPartiesMember_019fdc15-c471-76b2-915a-7e32107710fd" xlink:href="afg-20260930.xsd#afg_ManagedbyThirdPartiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7962-bb0a-cd11d9f17ede" xlink:to="loc_afg_ManagedbyThirdPartiesMember_019fdc15-c471-76b2-915a-7e32107710fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7f27-bdee-9d0785eb1c4f" 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_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-7be8-b43b-ea8363fb7bda" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019fdc15-c471-7f27-bdee-9d0785eb1c4f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7f27-bdee-9d0785eb1c4f_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_019fdc15-c471-7f27-bdee-9d0785eb1c4f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7f27-bdee-9d0785eb1c4f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7bc0-a4c4-848b2d9679a4" 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_019fdc15-c471-7f27-bdee-9d0785eb1c4f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7bc0-a4c4-848b2d9679a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c471-76bb-bd40-ec57e5a69fcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollateralizedLoanObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019fdc15-c471-7bc0-a4c4-848b2d9679a4" xlink:to="loc_us-gaap_CollateralizedLoanObligationsMember_019fdc15-c471-76bb-bd40-ec57e5a69fcd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PercentageOfInvestmentOfMostSubordinateDebtTrancheOfVariableInterestEntityMinimum_019fdc15-c471-73d9-b67f-ab2eb00ea6fa" xlink:href="afg-20260930.xsd#afg_PercentageOfInvestmentOfMostSubordinateDebtTrancheOfVariableInterestEntityMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_PercentageOfInvestmentOfMostSubordinateDebtTrancheOfVariableInterestEntityMinimum_019fdc15-c471-73d9-b67f-ab2eb00ea6fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_PercentageOfInvestmentOfMostSubordinateDebtTrancheOfVariableInterestEntityMaximum_019fdc15-c471-775f-89ec-96d95b19a9f4" xlink:href="afg-20260930.xsd#afg_PercentageOfInvestmentOfMostSubordinateDebtTrancheOfVariableInterestEntityMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_PercentageOfInvestmentOfMostSubordinateDebtTrancheOfVariableInterestEntityMaximum_019fdc15-c471-775f-89ec-96d95b19a9f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NumberOfCollateralizedLoanObligationEntities_019fdc15-c471-7539-b183-795ed07d8971" xlink:href="afg-20260930.xsd#afg_NumberOfCollateralizedLoanObligationEntities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_NumberOfCollateralizedLoanObligationEntities_019fdc15-c471-7539-b183-795ed07d8971" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_019fdc15-c471-7e1e-8551-54bf534cd55a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_019fdc15-c471-7e1e-8551-54bf534cd55a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NumberOfCollateralizedLoanObligationEntitiesFormedDuringThePeriod_019fdc15-c471-743b-af3b-8132cd458c68" xlink:href="afg-20260930.xsd#afg_NumberOfCollateralizedLoanObligationEntitiesFormedDuringThePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_NumberOfCollateralizedLoanObligationEntitiesFormedDuringThePeriod_019fdc15-c471-743b-af3b-8132cd458c68" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_FaceValueOfLiabilitiesIssuedByManagedInvestmentEntitiesOnIssuanceDate_019fdc15-c471-70cf-b997-334670dfb782" xlink:href="afg-20260930.xsd#afg_FaceValueOfLiabilitiesIssuedByManagedInvestmentEntitiesOnIssuanceDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_FaceValueOfLiabilitiesIssuedByManagedInvestmentEntitiesOnIssuanceDate_019fdc15-c471-70cf-b997-334670dfb782" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_FaceAmountOfManagedInvestmentEntitiesLiabilitiesPurchasedAtIssuanceDate_019fdc15-c471-7ef1-b09d-dc85a52bcdf1" xlink:href="afg-20260930.xsd#afg_FaceAmountOfManagedInvestmentEntitiesLiabilitiesPurchasedAtIssuanceDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_FaceAmountOfManagedInvestmentEntitiesLiabilitiesPurchasedAtIssuanceDate_019fdc15-c471-7ef1-b09d-dc85a52bcdf1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NumberOfCollateralizedLoanObligationEntitiesSubstantiallyLiquidatedDuringThePeriod_019fdc15-c471-7712-92a2-32d76d4ce329" xlink:href="afg-20260930.xsd#afg_NumberOfCollateralizedLoanObligationEntitiesSubstantiallyLiquidatedDuringThePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_NumberOfCollateralizedLoanObligationEntitiesSubstantiallyLiquidatedDuringThePeriod_019fdc15-c471-7712-92a2-32d76d4ce329" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DifferenceBetweenAggregateUnpaidPrincipalBalanceAndFairValueOfVariableInterestEntityInvestments_019fdc15-c471-74dd-a0ab-50d19fcc3f4d" xlink:href="afg-20260930.xsd#afg_DifferenceBetweenAggregateUnpaidPrincipalBalanceAndFairValueOfVariableInterestEntityInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_DifferenceBetweenAggregateUnpaidPrincipalBalanceAndFairValueOfVariableInterestEntityInvestments_019fdc15-c471-74dd-a0ab-50d19fcc3f4d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_DifferenceBetweenAggregateUnpaidPrincipalBalanceAndFairValueOfVariableInterestEntityDebt_019fdc15-c471-73ad-aaf5-08d06892cf2c" xlink:href="afg-20260930.xsd#afg_DifferenceBetweenAggregateUnpaidPrincipalBalanceAndFairValueOfVariableInterestEntityDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_DifferenceBetweenAggregateUnpaidPrincipalBalanceAndFairValueOfVariableInterestEntityDebt_019fdc15-c471-73ad-aaf5-08d06892cf2c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_CarryingAmountOfVariableInterestEntityLoansInDefault_019fdc15-c471-7ac8-95eb-d74be9a10919" xlink:href="afg-20260930.xsd#afg_CarryingAmountOfVariableInterestEntityLoansInDefault"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_afg_CarryingAmountOfVariableInterestEntityLoansInDefault_019fdc15-c471-7ac8-95eb-d74be9a10919" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c471-70ba-92f7-c8c1ff900787" 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_VariableInterestEntityLineItems_019fdc15-c471-7949-9ee3-899f6f3afe1e" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fdc15-c471-70ba-92f7-c8c1ff900787" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/ManagedInvestmentEntitiesProgressionofinvestmentinCLOtranchesDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#ManagedInvestmentEntitiesProgressionofinvestmentinCLOtranchesDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/ManagedInvestmentEntitiesProgressionofinvestmentinCLOtranchesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-718d-aad3-a96910cd06ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-7003-880e-11d004c12a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-718d-aad3-a96910cd06ab" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-7003-880e-11d004c12a6f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-7dee-869a-1884bf6700ce" 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_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-7003-880e-11d004c12a6f" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-7dee-869a-1884bf6700ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7dee-869a-1884bf6700ce_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_019fdc15-c471-7dee-869a-1884bf6700ce" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7dee-869a-1884bf6700ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7a49-9dc8-9e7753a7aede" 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_019fdc15-c471-7dee-869a-1884bf6700ce" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7a49-9dc8-9e7753a7aede" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019fdc15-c471-7c28-8d52-2bf9ea847f2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7a49-9dc8-9e7753a7aede" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019fdc15-c471-7c28-8d52-2bf9ea847f2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_VariableInterestEntityOwnershipRollForward_019fdc15-c471-7fb6-934e-032134e16ac3" xlink:href="afg-20260930.xsd#afg_VariableInterestEntityOwnershipRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-718d-aad3-a96910cd06ab" xlink:to="loc_afg_VariableInterestEntityOwnershipRollForward_019fdc15-c471-7fb6-934e-032134e16ac3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMaximumLossExposureAmount_019fdc15-c471-7329-8f4c-3cb7643b0eb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMaximumLossExposureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_VariableInterestEntityOwnershipRollForward_019fdc15-c471-7fb6-934e-032134e16ac3" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMaximumLossExposureAmount_019fdc15-c471-7329-8f4c-3cb7643b0eb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_AmountOfManagedInvestmentEntitiesLiabilitiesPurchasedDuringThePeriod_019fdc15-c471-7fbc-9ae4-d3574ec647cc" xlink:href="afg-20260930.xsd#afg_AmountOfManagedInvestmentEntitiesLiabilitiesPurchasedDuringThePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_VariableInterestEntityOwnershipRollForward_019fdc15-c471-7fb6-934e-032134e16ac3" xlink:to="loc_afg_AmountOfManagedInvestmentEntitiesLiabilitiesPurchasedDuringThePeriod_019fdc15-c471-7fbc-9ae4-d3574ec647cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_ProceedsReceivedRelatedToSalesOfManagedInvestmentEntitiesLiabilities_019fdc15-c471-7f7e-9fd2-33a09a86b5e4" xlink:href="afg-20260930.xsd#afg_ProceedsReceivedRelatedToSalesOfManagedInvestmentEntitiesLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_VariableInterestEntityOwnershipRollForward_019fdc15-c471-7fb6-934e-032134e16ac3" xlink:to="loc_afg_ProceedsReceivedRelatedToSalesOfManagedInvestmentEntitiesLiabilities_019fdc15-c471-7f7e-9fd2-33a09a86b5e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_ProceedsReceivedFromDistributionsOfManagedInvestmentEntitiesLiabilities_019fdc15-c471-7391-a486-1b8da72924ec" xlink:href="afg-20260930.xsd#afg_ProceedsReceivedFromDistributionsOfManagedInvestmentEntitiesLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_VariableInterestEntityOwnershipRollForward_019fdc15-c471-7fb6-934e-032134e16ac3" xlink:to="loc_afg_ProceedsReceivedFromDistributionsOfManagedInvestmentEntitiesLiabilities_019fdc15-c471-7391-a486-1b8da72924ec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_EarningsLossesOfVariableInterestEntitiesAttributableToShareholders_019fdc15-c471-7457-bd02-12fd377c98a1" xlink:href="afg-20260930.xsd#afg_EarningsLossesOfVariableInterestEntitiesAttributableToShareholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_VariableInterestEntityOwnershipRollForward_019fdc15-c471-7fb6-934e-032134e16ac3" xlink:to="loc_afg_EarningsLossesOfVariableInterestEntitiesAttributableToShareholders_019fdc15-c471-7457-bd02-12fd377c98a1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMaximumLossExposureAmount_019fdc15-c471-7006-8d4d-6ac6ebcc9051" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMaximumLossExposureAmount"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/ManagedInvestmentEntitiesSelectedfinancialinformationrelatedtoCLOsDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#ManagedInvestmentEntitiesSelectedfinancialinformationrelatedtoCLOsDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/ManagedInvestmentEntitiesSelectedfinancialinformationrelatedtoCLOsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7d33-9e06-93ea8632a054" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-73f8-bf70-c9aead9c136c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7d33-9e06-93ea8632a054" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-73f8-bf70-c9aead9c136c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-7269-b9ef-c7973a87e031" 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_ScheduleOfVariableInterestEntitiesTable_019fdc15-c471-73f8-bf70-c9aead9c136c" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-7269-b9ef-c7973a87e031" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7269-b9ef-c7973a87e031_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_019fdc15-c471-7269-b9ef-c7973a87e031" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7269-b9ef-c7973a87e031_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7d2c-a47a-38db96e89f5c" 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_019fdc15-c471-7269-b9ef-c7973a87e031" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7d2c-a47a-38db96e89f5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019fdc15-c471-79fa-a8b2-307d234a47cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7d2c-a47a-38db96e89f5c" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019fdc15-c471-79fa-a8b2-307d234a47cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_FinancialInformationRelatedToCollateralizedLoanObligationsAbstract_019fdc15-c471-778e-a4f4-f7f1f590a404" xlink:href="afg-20260930.xsd#afg_FinancialInformationRelatedToCollateralizedLoanObligationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019fdc15-c471-7d33-9e06-93ea8632a054" xlink:to="loc_afg_FinancialInformationRelatedToCollateralizedLoanObligationsAbstract_019fdc15-c471-778e-a4f4-f7f1f590a404" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_GainsLossesOnChangeInFairValueOfAssetsLiabilitiesOfCollateralizedLoanObligationsAbstract_019fdc15-c471-74a4-ae1b-21ada4e6a3f3" xlink:href="afg-20260930.xsd#afg_GainsLossesOnChangeInFairValueOfAssetsLiabilitiesOfCollateralizedLoanObligationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_FinancialInformationRelatedToCollateralizedLoanObligationsAbstract_019fdc15-c471-778e-a4f4-f7f1f590a404" xlink:to="loc_afg_GainsLossesOnChangeInFairValueOfAssetsLiabilitiesOfCollateralizedLoanObligationsAbstract_019fdc15-c471-74a4-ae1b-21ada4e6a3f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_GainLossOnChangeInFairValueOfAssetsOfVariableInterestEntities_019fdc15-c471-722a-96d9-77da37a58dd1" xlink:href="afg-20260930.xsd#afg_GainLossOnChangeInFairValueOfAssetsOfVariableInterestEntities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_GainsLossesOnChangeInFairValueOfAssetsLiabilitiesOfCollateralizedLoanObligationsAbstract_019fdc15-c471-74a4-ae1b-21ada4e6a3f3" xlink:to="loc_afg_GainLossOnChangeInFairValueOfAssetsOfVariableInterestEntities_019fdc15-c471-722a-96d9-77da37a58dd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_GainLossOnChangeInFairValueOfLiabilitiesOfVariableInterestEntities_019fdc15-c471-7f2c-b5a6-45d484a5a9de" xlink:href="afg-20260930.xsd#afg_GainLossOnChangeInFairValueOfLiabilitiesOfVariableInterestEntities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_GainsLossesOnChangeInFairValueOfAssetsLiabilitiesOfCollateralizedLoanObligationsAbstract_019fdc15-c471-74a4-ae1b-21ada4e6a3f3" xlink:to="loc_afg_GainLossOnChangeInFairValueOfLiabilitiesOfVariableInterestEntities_019fdc15-c471-7f2c-b5a6-45d484a5a9de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_ManagementFeesPaidByVariableInterestEntities_019fdc15-c471-7130-b235-2a97b95d2ba6" xlink:href="afg-20260930.xsd#afg_ManagementFeesPaidByVariableInterestEntities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_FinancialInformationRelatedToCollateralizedLoanObligationsAbstract_019fdc15-c471-778e-a4f4-f7f1f590a404" xlink:to="loc_afg_ManagementFeesPaidByVariableInterestEntities_019fdc15-c471-7130-b235-2a97b95d2ba6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_EarningsLossesOfVariableInterestEntitiesAttributableToShareholders_019fdc15-c471-77c4-9c5b-d138cad60414" xlink:href="afg-20260930.xsd#afg_EarningsLossesOfVariableInterestEntitiesAttributableToShareholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_FinancialInformationRelatedToCollateralizedLoanObligationsAbstract_019fdc15-c471-778e-a4f4-f7f1f590a404" xlink:to="loc_afg_EarningsLossesOfVariableInterestEntitiesAttributableToShareholders_019fdc15-c471-77c4-9c5b-d138cad60414" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/LongTermDebtScheduleoflongtermdebtDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#LongTermDebtScheduleoflongtermdebtDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/LongTermDebtScheduleoflongtermdebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fdc15-c471-7b9d-a9f3-ecda0230686e" 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_019fdc15-c471-76ba-ad99-624f711989ff" 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_019fdc15-c471-7b9d-a9f3-ecda0230686e" xlink:to="loc_us-gaap_DebtInstrumentTable_019fdc15-c471-76ba-ad99-624f711989ff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019fdc15-c471-73a9-b2ac-dc0518a0adda" 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_019fdc15-c471-76ba-ad99-624f711989ff" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019fdc15-c471-73a9-b2ac-dc0518a0adda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fdc15-c471-73a9-b2ac-dc0518a0adda_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_019fdc15-c471-73a9-b2ac-dc0518a0adda" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fdc15-c471-73a9-b2ac-dc0518a0adda_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019fdc15-c471-7f6b-9621-bf707a1989d1" 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_019fdc15-c471-73a9-b2ac-dc0518a0adda" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019fdc15-c471-7f6b-9621-bf707a1989d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019fdc15-c471-77ad-b980-a2b2e9f5a29d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019fdc15-c471-7f6b-9621-bf707a1989d1" xlink:to="loc_us-gaap_SeniorNotesMember_019fdc15-c471-77ad-b980-a2b2e9f5a29d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_019fdc15-c471-735d-8a74-45a29202f7da" 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_019fdc15-c471-7f6b-9621-bf707a1989d1" xlink:to="loc_us-gaap_SubordinatedDebtMember_019fdc15-c471-735d-8a74-45a29202f7da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019fdc15-c471-7e04-be31-7eb44a3038b7" 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_019fdc15-c471-76ba-ad99-624f711989ff" xlink:to="loc_us-gaap_DebtInstrumentAxis_019fdc15-c471-7e04-be31-7eb44a3038b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7e04-be31-7eb44a3038b7_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_019fdc15-c471-7e04-be31-7eb44a3038b7" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7e04-be31-7eb44a3038b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" 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_019fdc15-c471-7e04-be31-7eb44a3038b7" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SeniorNotesDueInJune2047Member_019fdc15-c471-7925-b860-b25279d09af3" xlink:href="afg-20260930.xsd#afg_SeniorNotesDueInJune2047Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:to="loc_afg_SeniorNotesDueInJune2047Member_019fdc15-c471-7925-b860-b25279d09af3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SeniorNotesDueInSeptember2035Member_019fdc15-c471-7e27-ba11-a3a45a1bcc91" xlink:href="afg-20260930.xsd#afg_SeniorNotesDueInSeptember2035Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:to="loc_afg_SeniorNotesDueInSeptember2035Member_019fdc15-c471-7e27-ba11-a3a45a1bcc91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SeniorNotesDueInApril2030Member_019fdc15-c471-7c2a-bda8-0812ad687380" xlink:href="afg-20260930.xsd#afg_SeniorNotesDueInApril2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:to="loc_afg_SeniorNotesDueInApril2030Member_019fdc15-c471-7c2a-bda8-0812ad687380" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_OtherLongtermDebtMember_019fdc15-c471-7240-b4e7-437e065b2b0e" xlink:href="afg-20260930.xsd#afg_OtherLongtermDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:to="loc_afg_OtherLongtermDebtMember_019fdc15-c471-7240-b4e7-437e065b2b0e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SubordinatedDebenturesDueInSeptember2060Member_019fdc15-c471-7b69-bdbe-1990af00c892" xlink:href="afg-20260930.xsd#afg_SubordinatedDebenturesDueInSeptember2060Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:to="loc_afg_SubordinatedDebenturesDueInSeptember2060Member_019fdc15-c471-7b69-bdbe-1990af00c892" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SubordinatedDebenturesdueinDecember2059Member_019fdc15-c471-7c08-bf00-17c8af4ae269" xlink:href="afg-20260930.xsd#afg_SubordinatedDebenturesdueinDecember2059Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:to="loc_afg_SubordinatedDebenturesdueinDecember2059Member_019fdc15-c471-7c08-bf00-17c8af4ae269" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SubordinatedDebenturesDueInJune2060Member_019fdc15-c471-7402-bc7a-464499dcfc38" xlink:href="afg-20260930.xsd#afg_SubordinatedDebenturesDueInJune2060Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:to="loc_afg_SubordinatedDebenturesDueInJune2060Member_019fdc15-c471-7402-bc7a-464499dcfc38" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SubordinatedDebenturesDueInMarch2059Member_019fdc15-c471-7683-9bae-560e6b82812b" xlink:href="afg-20260930.xsd#afg_SubordinatedDebenturesDueInMarch2059Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019fdc15-c471-7b39-bc37-41cd4ca489ab" xlink:to="loc_afg_SubordinatedDebenturesDueInMarch2059Member_019fdc15-c471-7683-9bae-560e6b82812b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-738b-a5ac-a064f4bbbf05" 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_019fdc15-c471-76ba-ad99-624f711989ff" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-738b-a5ac-a064f4bbbf05" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-738b-a5ac-a064f4bbbf05_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_019fdc15-c471-738b-a5ac-a064f4bbbf05" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-738b-a5ac-a064f4bbbf05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-70b0-895a-fbef78872797" 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_019fdc15-c471-738b-a5ac-a064f4bbbf05" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-70b0-895a-fbef78872797" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_019fdc15-c471-7cbf-a945-46e5c4bfc7ee" 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_019fdc15-c471-70b0-895a-fbef78872797" xlink:to="loc_srt_ParentCompanyMember_019fdc15-c471-7cbf-a945-46e5c4bfc7ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fdc15-c471-7826-863b-533306ba2e89" 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_019fdc15-c471-7b9d-a9f3-ecda0230686e" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019fdc15-c471-7826-863b-533306ba2e89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_SummaryOfCarryingValueOfLongTermDebtAbstract_019fdc15-c471-7cc0-9b90-f5aa49aba3bc" xlink:href="afg-20260930.xsd#afg_SummaryOfCarryingValueOfLongTermDebtAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fdc15-c471-7b9d-a9f3-ecda0230686e" xlink:to="loc_afg_SummaryOfCarryingValueOfLongTermDebtAbstract_019fdc15-c471-7cc0-9b90-f5aa49aba3bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019fdc15-c471-78c4-bb9c-d80bde051aec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SummaryOfCarryingValueOfLongTermDebtAbstract_019fdc15-c471-7cc0-9b90-f5aa49aba3bc" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019fdc15-c471-78c4-bb9c-d80bde051aec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019fdc15-c471-7c2f-9e1c-fed508f75e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SummaryOfCarryingValueOfLongTermDebtAbstract_019fdc15-c471-7cc0-9b90-f5aa49aba3bc" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019fdc15-c471-7c2f-9e1c-fed508f75e3b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019fdc15-c471-7e32-9107-fce736978abc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_afg_SummaryOfCarryingValueOfLongTermDebtAbstract_019fdc15-c471-7cc0-9b90-f5aa49aba3bc" xlink:to="loc_us-gaap_LongTermDebt_019fdc15-c471-7e32-9107-fce736978abc" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/LongTermDebtNarrativeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#LongTermDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/LongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019fdc15-c471-77f2-b138-1f3fcf6c852f" 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_019fdc15-c471-7461-863d-88881ffc75c3" 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_019fdc15-c471-77f2-b138-1f3fcf6c852f" xlink:to="loc_us-gaap_DebtInstrumentTable_019fdc15-c471-7461-863d-88881ffc75c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-7401-ac57-290b6edec926" 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_019fdc15-c471-7461-863d-88881ffc75c3" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019fdc15-c471-7401-ac57-290b6edec926" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7401-ac57-290b6edec926_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_019fdc15-c471-7401-ac57-290b6edec926" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7401-ac57-290b6edec926_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7e61-92a2-2a55af57b074" 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_019fdc15-c471-7401-ac57-290b6edec926" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019fdc15-c471-7e61-92a2-2a55af57b074" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_019fdc15-c471-7e6b-b34e-ac2abae02f0c" 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_019fdc15-c471-7e61-92a2-2a55af57b074" xlink:to="loc_srt_ParentCompanyMember_019fdc15-c471-7e6b-b34e-ac2abae02f0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019fdc15-c471-745b-ad5f-92e8f539aba3" 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_019fdc15-c471-7461-863d-88881ffc75c3" xlink:to="loc_srt_RangeAxis_019fdc15-c471-745b-ad5f-92e8f539aba3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fdc15-c471-745b-ad5f-92e8f539aba3_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_019fdc15-c471-745b-ad5f-92e8f539aba3" xlink:to="loc_srt_RangeMember_019fdc15-c471-745b-ad5f-92e8f539aba3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019fdc15-c471-7835-86d4-55ddc037feaa" 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_019fdc15-c471-745b-ad5f-92e8f539aba3" xlink:to="loc_srt_RangeMember_019fdc15-c471-7835-86d4-55ddc037feaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019fdc15-c471-7197-81fa-e13532ebba31" 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_019fdc15-c471-7835-86d4-55ddc037feaa" xlink:to="loc_srt_MinimumMember_019fdc15-c471-7197-81fa-e13532ebba31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019fdc15-c471-7c50-bed5-bac24b2a7bcd" 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_019fdc15-c471-7835-86d4-55ddc037feaa" xlink:to="loc_srt_MaximumMember_019fdc15-c471-7c50-bed5-bac24b2a7bcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtByMaturityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fdc15-c471-77f2-b138-1f3fcf6c852f" xlink:to="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_019fdc15-c471-7389-a19b-43a372e05b0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_019fdc15-c471-7389-a19b-43a372e05b0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_019fdc15-c471-73f9-8301-0e6e36427ce9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_019fdc15-c471-73f9-8301-0e6e36427ce9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_019fdc15-c471-7d65-a72b-86cc069ef85c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_019fdc15-c471-7d65-a72b-86cc069ef85c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_019fdc15-c471-7f0e-974d-35a800ff7d20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_019fdc15-c471-7f0e-974d-35a800ff7d20" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_019fdc15-c471-7266-a171-09e65a14abf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_019fdc15-c471-7266-a171-09e65a14abf6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_019fdc15-c471-76da-96ec-4f205bcbecdd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_019fdc15-c471-76da-96ec-4f205bcbecdd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_019fdc15-c471-72f1-8f49-cc5a8fa6fa56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract_019fdc15-c471-712e-b5df-b63cddee893f" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_019fdc15-c471-72f1-8f49-cc5a8fa6fa56" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019fdc15-c471-77f5-9cd3-d54bf066b885" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fdc15-c471-77f2-b138-1f3fcf6c852f" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019fdc15-c471-77f5-9cd3-d54bf066b885" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fdc15-c471-7ee5-8550-dc1027ac3625" 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_019fdc15-c471-77f2-b138-1f3fcf6c852f" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019fdc15-c471-7ee5-8550-dc1027ac3625" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration_019fdc15-c471-7fb4-b3f5-b3532da4692c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019fdc15-c471-77f2-b138-1f3fcf6c852f" xlink:to="loc_us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration_019fdc15-c471-7fb4-b3f5-b3532da4692c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019fdc15-c471-7607-b70c-0a0e2d60d80b" 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_DebtInstrumentLineItems_019fdc15-c471-77f2-b138-1f3fcf6c852f" xlink:to="loc_us-gaap_LineOfCredit_019fdc15-c471-7607-b70c-0a0e2d60d80b" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/ShareholdersEquityPreferredstockauthorizedforissuanceDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#ShareholdersEquityPreferredstockauthorizedforissuanceDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/ShareholdersEquityPreferredstockauthorizedforissuanceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019fdc15-c471-7a51-baed-d06232c6dd9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019fdc15-c471-7dc2-9852-8f4202578a1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019fdc15-c471-7a51-baed-d06232c6dd9b" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019fdc15-c471-7dc2-9852-8f4202578a1b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019fdc15-c471-7698-8c36-801106ea0af5" 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_us-gaap_ScheduleOfStockByClassTable_019fdc15-c471-7dc2-9852-8f4202578a1b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019fdc15-c471-7698-8c36-801106ea0af5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fdc15-c471-7698-8c36-801106ea0af5_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_019fdc15-c471-7698-8c36-801106ea0af5" xlink:to="loc_us-gaap_ClassOfStockDomain_019fdc15-c471-7698-8c36-801106ea0af5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019fdc15-c471-7627-8e05-d87a34499a4f" 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_019fdc15-c471-7698-8c36-801106ea0af5" xlink:to="loc_us-gaap_ClassOfStockDomain_019fdc15-c471-7627-8e05-d87a34499a4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_VotingPreferredStockMember_019fdc15-c471-7d17-a6fb-0f932efef495" xlink:href="afg-20260930.xsd#afg_VotingPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fdc15-c471-7627-8e05-d87a34499a4f" xlink:to="loc_afg_VotingPreferredStockMember_019fdc15-c471-7d17-a6fb-0f932efef495" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_NonvotingPreferredStockMember_019fdc15-c471-734f-8fe7-be7c7fa98c71" xlink:href="afg-20260930.xsd#afg_NonvotingPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019fdc15-c471-7627-8e05-d87a34499a4f" xlink:to="loc_afg_NonvotingPreferredStockMember_019fdc15-c471-734f-8fe7-be7c7fa98c71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019fdc15-c471-7bbb-b6f8-0668f52ab31a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019fdc15-c471-7a51-baed-d06232c6dd9b" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019fdc15-c471-7bbb-b6f8-0668f52ab31a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/ShareholdersEquityProgressionofthecomponentsofaccumulatedothercomprehensiveincomeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#ShareholdersEquityProgressionofthecomponentsofaccumulatedothercomprehensiveincomeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/ShareholdersEquityProgressionofthecomponentsofaccumulatedothercomprehensiveincomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" 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_019fdc15-c471-7f9f-85a0-8c8768669eb8" 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_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019fdc15-c471-7f9f-85a0-8c8768669eb8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019fdc15-c471-7f4d-8b9a-332452626cc5" 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_019fdc15-c471-7f9f-85a0-8c8768669eb8" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019fdc15-c471-7f4d-8b9a-332452626cc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fdc15-c471-7f4d-8b9a-332452626cc5_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_019fdc15-c471-7f4d-8b9a-332452626cc5" xlink:to="loc_us-gaap_EquityComponentDomain_019fdc15-c471-7f4d-8b9a-332452626cc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019fdc15-c471-7f6b-aa0d-b6268ece4c59" 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_019fdc15-c471-7f4d-8b9a-332452626cc5" xlink:to="loc_us-gaap_EquityComponentDomain_019fdc15-c471-7f6b-aa0d-b6268ece4c59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fdc15-c471-7e9b-acd3-dbee4481c278" 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_019fdc15-c471-7f6b-aa0d-b6268ece4c59" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fdc15-c471-7e9b-acd3-dbee4481c278" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019fdc15-c471-7695-9471-85902db91566" 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_019fdc15-c471-7e9b-acd3-dbee4481c278" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019fdc15-c471-7695-9471-85902db91566" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019fdc15-c471-7413-8925-83ae3f948ee4" 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_019fdc15-c471-7e9b-acd3-dbee4481c278" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019fdc15-c471-7413-8925-83ae3f948ee4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019fdc15-c471-7b81-9a46-874025a7a28f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fdc15-c471-7e9b-acd3-dbee4481c278" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019fdc15-c471-7b81-9a46-874025a7a28f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019fdc15-c471-7ee3-aabc-f3f30c161b79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019fdc15-c471-7e9b-acd3-dbee4481c278" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019fdc15-c471-7ee3-aabc-f3f30c161b79" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fdc15-c471-7412-b678-0223d9a7b575" 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_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fdc15-c471-7412-b678-0223d9a7b575" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fdc15-c471-77f3-a80f-eaf909a13b89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fdc15-c471-7412-b678-0223d9a7b575" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fdc15-c471-77f3-a80f-eaf909a13b89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_019fdc15-c471-7b56-94bc-868e37c45cc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fdc15-c471-7412-b678-0223d9a7b575" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_019fdc15-c471-7b56-94bc-868e37c45cc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_019fdc15-c471-7dad-b290-ed676cb23e52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fdc15-c471-7412-b678-0223d9a7b575" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_019fdc15-c471-7dad-b290-ed676cb23e52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019fdc15-c471-7b71-a5ee-3393b5bc3b64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019fdc15-c471-7412-b678-0223d9a7b575" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019fdc15-c471-7b71-a5ee-3393b5bc3b64" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019fdc15-c471-7913-ae4c-c9781dfdb808" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesUnrealizedGainLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax_019fdc15-c471-7a49-9e31-d7ac4a159560" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax_019fdc15-c471-7a49-9e31-d7ac4a159560" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax_019fdc15-c471-7ee3-9fc6-ecf7b9e83815" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax_019fdc15-c471-7ee3-9fc6-ecf7b9e83815" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019fdc15-c471-75b9-bbfa-5a38e7a51c0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019fdc15-c471-75b9-bbfa-5a38e7a51c0b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax_019fdc15-c471-70db-9f83-b092977ddbd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax_019fdc15-c471-70db-9f83-b092977ddbd2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax_019fdc15-c471-7d94-a10f-b72cd7593391" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax_019fdc15-c471-7d94-a10f-b72cd7593391" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax_019fdc15-c471-7590-905c-f54a52dcf265" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax_019fdc15-c471-7590-905c-f54a52dcf265" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax_019fdc15-c471-78c5-b03e-8ad2725e94b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax_019fdc15-c471-78c5-b03e-8ad2725e94b6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax_019fdc15-c471-79f7-97e5-e77b12f8808e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax_019fdc15-c471-79f7-97e5-e77b12f8808e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019fdc15-c471-7ec5-bdc1-ee822096d937" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesUnrealizedGainLossAbstract_019fdc15-c471-789f-bc77-0ad7762067b3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_019fdc15-c471-7ec5-bdc1-ee822096d937" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019fdc15-c471-7da2-af0b-1f33873f77e8" 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_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019fdc15-c471-7da2-af0b-1f33873f77e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax_019fdc15-c471-7ccf-914a-d2ffdf799248" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax_019fdc15-c471-7ccf-914a-d2ffdf799248" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019fdc15-c471-7325-9cb3-5064401cc38d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019fdc15-c471-7325-9cb3-5064401cc38d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019fdc15-c471-7af8-ad80-46cd863fc001" 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_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019fdc15-c471-7af8-ad80-46cd863fc001" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019fdc15-c471-7a50-8965-79b5104c17fa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019fdc15-c471-7a50-8965-79b5104c17fa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019fdc15-c471-7b16-b2ac-aaba6ed14cc8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019fdc15-c471-7b16-b2ac-aaba6ed14cc8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax_019fdc15-c471-7216-9c37-08cc8b08ae33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax_019fdc15-c471-7216-9c37-08cc8b08ae33" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTax_019fdc15-c471-727e-981d-f72c2058e7b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTax_019fdc15-c471-727e-981d-f72c2058e7b8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019fdc15-c471-73b5-ace1-cb4d1fa48ee6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOfCashFlowHedgeGainLossAbstract_019fdc15-c471-7fc0-8c3a-2da986b6e71a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_019fdc15-c471-73b5-ace1-cb4d1fa48ee6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax_019fdc15-c471-77d9-ad05-12fe2380c796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax_019fdc15-c471-77d9-ad05-12fe2380c796" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax_019fdc15-c471-70cf-8573-7d9201c1cd06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax_019fdc15-c471-70cf-8573-7d9201c1cd06" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019fdc15-c471-72ba-aa55-1facb0ff1d17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019fdc15-c471-72ba-aa55-1facb0ff1d17" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax_019fdc15-c471-7cc5-9ddb-009bfa0d951c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax_019fdc15-c471-7cc5-9ddb-009bfa0d951c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax_019fdc15-c471-7e7b-9e28-b2bce741bde0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax_019fdc15-c471-7e7b-9e28-b2bce741bde0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019fdc15-c471-719c-9eb7-f89e8510ea4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019fdc15-c471-78f9-a044-975546cc1e52" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_019fdc15-c471-719c-9eb7-f89e8510ea4d" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/ShareholdersEquityNarrativeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#ShareholdersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/ShareholdersEquityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fdc15-c471-7e54-a1b6-d1aa520954da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fdc15-c471-711a-bb3d-3bfa95634674" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fdc15-c471-7e54-a1b6-d1aa520954da" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fdc15-c471-711a-bb3d-3bfa95634674" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019fdc15-c471-7026-ae55-88050c59bf05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019fdc15-c471-711a-bb3d-3bfa95634674" xlink:to="loc_us-gaap_AwardTypeAxis_019fdc15-c471-7026-ae55-88050c59bf05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fdc15-c471-7026-ae55-88050c59bf05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019fdc15-c471-7026-ae55-88050c59bf05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fdc15-c471-7026-ae55-88050c59bf05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fdc15-c471-78ff-9683-cd21b474bfaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019fdc15-c471-7026-ae55-88050c59bf05" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fdc15-c471-78ff-9683-cd21b474bfaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019fdc15-c471-7af1-8483-66dec33ff11d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fdc15-c471-78ff-9683-cd21b474bfaf" xlink:to="loc_us-gaap_RestrictedStockMember_019fdc15-c471-7af1-8483-66dec33ff11d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockCompensationPlanMember_019fdc15-c471-785e-9b39-0890c8e4f3f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019fdc15-c471-78ff-9683-cd21b474bfaf" xlink:to="loc_us-gaap_StockCompensationPlanMember_019fdc15-c471-785e-9b39-0890c8e4f3f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019fdc15-c471-76b9-bccf-56f55a2e8db3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fdc15-c471-7e54-a1b6-d1aa520954da" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_019fdc15-c471-76b9-bccf-56f55a2e8db3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019fdc15-c471-7b58-9196-5d6f35071240" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fdc15-c471-7e54-a1b6-d1aa520954da" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019fdc15-c471-7b58-9196-5d6f35071240" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fdc15-c471-767e-98d4-dd5ca75ad703" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019fdc15-c471-7e54-a1b6-d1aa520954da" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019fdc15-c471-767e-98d4-dd5ca75ad703" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.afginc.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="afg-20260930.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.afginc.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019fdc15-c517-72c5-ab8a-55b8ea8b6613" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019fdc15-c517-7568-94e5-5834dbe04a66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019fdc15-c517-72c5-ab8a-55b8ea8b6613" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019fdc15-c517-7568-94e5-5834dbe04a66" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019fdc15-c517-7b4c-91ff-4e08923625ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019fdc15-c517-7568-94e5-5834dbe04a66" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019fdc15-c517-7b4c-91ff-4e08923625ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019fdc15-c517-7b4c-91ff-4e08923625ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019fdc15-c517-7b4c-91ff-4e08923625ad" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019fdc15-c517-7b4c-91ff-4e08923625ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019fdc15-c517-7a20-8bec-f4651678ae61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019fdc15-c517-7b4c-91ff-4e08923625ad" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019fdc15-c517-7a20-8bec-f4651678ae61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_afg_Subsidiary1Member_019fdc15-c517-71a3-baf0-da161175317b" xlink:href="afg-20260930.xsd#afg_Subsidiary1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019fdc15-c517-7a20-8bec-f4651678ae61" xlink:to="loc_afg_Subsidiary1Member_019fdc15-c517-71a3-baf0-da161175317b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019fdc15-c517-7e92-8e27-a89c9ea6e363" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019fdc15-c517-72c5-ab8a-55b8ea8b6613" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019fdc15-c517-7e92-8e27-a89c9ea6e363" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes_019fdc15-c517-767d-8dc9-69e2e334925a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019fdc15-c517-72c5-ab8a-55b8ea8b6613" xlink:to="loc_us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes_019fdc15-c517-767d-8dc9-69e2e334925a" 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_AvailableForSaleSecuritiesDebtSecurities" 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_AssetsAbstract" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="arc" order="101"/>
  </link:definitionLink>
</link:linkbase>
