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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019c9670-f08a-7eaa-964c-d1b6784409f0,g:d08c1eeb-27ba-41fa-8193-4da9c7e854a9-->
<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://alight.com/role/Cover" xlink:type="simple" xlink:href="alit-20260331.xsd#Cover"/>
  <link:definitionLink xlink:role="http://alight.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019c9670-f330-7661-9aab-91893617bdc9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_DocumentInformationTable_019c9670-f330-7661-9aab-91893617bdc9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019c9670-f330-7548-9e61-97dd39f71f77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019c9670-f330-7661-9aab-91893617bdc9" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019c9670-f330-7548-9e61-97dd39f71f77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f330-7548-9e61-97dd39f71f77_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f330-7548-9e61-97dd39f71f77" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f330-7548-9e61-97dd39f71f77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f330-7f76-b36c-5e853a4940d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f330-7548-9e61-97dd39f71f77" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f330-7f76-b36c-5e853a4940d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019c9670-f330-7797-9433-21c28a3c47b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f330-7f76-b36c-5e853a4940d7" xlink:to="loc_us-gaap_CommonClassAMember_019c9670-f330-7797-9433-21c28a3c47b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassBOneMember_019c9670-f330-736b-9d32-6959024898d3" xlink:href="alit-20260331.xsd#alit_CommonClassBOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f330-7f76-b36c-5e853a4940d7" xlink:to="loc_alit_CommonClassBOneMember_019c9670-f330-736b-9d32-6959024898d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassBTwoMember_019c9670-f330-7934-ad38-0fbb070f7f8e" xlink:href="alit-20260331.xsd#alit_CommonClassBTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f330-7f76-b36c-5e853a4940d7" xlink:to="loc_alit_CommonClassBTwoMember_019c9670-f330-7934-ad38-0fbb070f7f8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassVMember_019c9670-f330-7627-99e2-1138fce40800" xlink:href="alit-20260331.xsd#alit_CommonClassVMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f330-7f76-b36c-5e853a4940d7" xlink:to="loc_alit_CommonClassVMember_019c9670-f330-7627-99e2-1138fce40800" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019c9670-f330-76f8-a59b-7b2a575a58fd" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_DocumentType_019c9670-f330-76f8-a59b-7b2a575a58fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019d0698-38e2-727e-8649-04c150534eb2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_DocumentQuarterlyReport_019d0698-38e2-727e-8649-04c150534eb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019c9670-f330-7ce8-a89a-8ac3b04fa1e9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_DocumentPeriodEndDate_019c9670-f330-7ce8-a89a-8ac3b04fa1e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019c9670-f330-73e3-865a-9c342696e4b0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_DocumentTransitionReport_019c9670-f330-73e3-865a-9c342696e4b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019c9670-f330-79d2-83c8-352deabd9065" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityFileNumber_019c9670-f330-79d2-83c8-352deabd9065" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019c9670-f330-76e1-85c3-6028120b84ca" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019c9670-f330-76e1-85c3-6028120b84ca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019c9670-f330-7b74-bf98-de91221033eb" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityTaxIdentificationNumber_019c9670-f330-7b74-bf98-de91221033eb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019c9670-f330-73b2-bfc7-dce1bc3fb373" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityAddressAddressLine1_019c9670-f330-73b2-bfc7-dce1bc3fb373" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019c9670-f330-74bb-9406-137e66a9eb17" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityAddressAddressLine2_019c9670-f330-74bb-9406-137e66a9eb17" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019c9670-f330-76b2-88b1-515468bfa583" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityAddressCityOrTown_019c9670-f330-76b2-88b1-515468bfa583" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019c9670-f330-74d3-ae71-b8e39d8e7e81" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityAddressStateOrProvince_019c9670-f330-74d3-ae71-b8e39d8e7e81" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019c9670-f330-7bb8-a24b-1d097774dca3" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityAddressPostalZipCode_019c9670-f330-7bb8-a24b-1d097774dca3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019c9670-f330-7218-8f26-a1f58a124d21" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_CityAreaCode_019c9670-f330-7218-8f26-a1f58a124d21" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019c9670-f330-733c-96e4-d1f6df3ed517" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_LocalPhoneNumber_019c9670-f330-733c-96e4-d1f6df3ed517" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019c9670-f330-7d43-a57e-3f7852a13105" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_Security12bTitle_019c9670-f330-7d43-a57e-3f7852a13105" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019c9670-f330-7ae7-ae24-79a391f13ae9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_TradingSymbol_019c9670-f330-7ae7-ae24-79a391f13ae9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019c9670-f330-7383-aa7d-948f503b4e78" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_SecurityExchangeName_019c9670-f330-7383-aa7d-948f503b4e78" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019c9670-f330-7714-abe5-dbe9b9ffdf65" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityCurrentReportingStatus_019c9670-f330-7714-abe5-dbe9b9ffdf65" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019c9670-f330-7f0c-9b94-b37ce9936aa9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityInteractiveDataCurrent_019c9670-f330-7f0c-9b94-b37ce9936aa9" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019c9670-f330-7f3b-8a1c-ca1efc041e1d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityFilerCategory_019c9670-f330-7f3b-8a1c-ca1efc041e1d" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019c9670-f330-70a2-a90a-fe87a0934ce1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntitySmallBusiness_019c9670-f330-70a2-a90a-fe87a0934ce1" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019c9670-f330-7c96-95c2-470826daaba9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityEmergingGrowthCompany_019c9670-f330-7c96-95c2-470826daaba9" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019c9670-f330-72da-8b72-5a9885ba610e" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityShellCompany_019c9670-f330-72da-8b72-5a9885ba610e" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019c9670-f330-7d18-b47a-45b6214ef396" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019c9670-f330-7d18-b47a-45b6214ef396" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019c9670-f331-7dc3-8a17-be50285814b1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_AmendmentFlag_019c9670-f331-7dc3-8a17-be50285814b1" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019c9670-f331-75fc-a4e1-2fd6577f2220" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_DocumentFiscalYearFocus_019c9670-f331-75fc-a4e1-2fd6577f2220" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019c9670-f331-719d-af8d-01cdd0db2dbc" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019c9670-f331-719d-af8d-01cdd0db2dbc" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019c9670-f331-77f9-9437-bb698ed26a90" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityCentralIndexKey_019c9670-f331-77f9-9437-bb698ed26a90" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019c9670-f330-7679-81b1-0229310f93a8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_CurrentFiscalYearEndDate_019c9670-f330-7679-81b1-0229310f93a8" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019c9670-f331-7304-9e24-c032a0d4a562" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019c9670-f330-7e3b-8cd5-07167f7fc3c0" xlink:to="loc_dei_EntityRegistrantName_019c9670-f331-7304-9e24-c032a0d4a562" xlink:type="arc" order="29"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="alit-20260331.xsd#CondensedConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://alight.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019c9670-f331-7f11-9339-6741169d45a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019c9670-f331-798c-a266-c88e87c87790" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7f11-9339-6741169d45a7" xlink:to="loc_us-gaap_StatementTable_019c9670-f331-798c-a266-c88e87c87790" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019c9670-f331-778b-aee4-443ae1ab4c1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019c9670-f331-798c-a266-c88e87c87790" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019c9670-f331-778b-aee4-443ae1ab4c1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f331-778b-aee4-443ae1ab4c1b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f331-778b-aee4-443ae1ab4c1b" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f331-778b-aee4-443ae1ab4c1b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7000-8826-276ca1253a37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f331-778b-aee4-443ae1ab4c1b" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7000-8826-276ca1253a37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019c9670-f331-7b4a-a1c8-5ab12318c2c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7000-8826-276ca1253a37" xlink:to="loc_us-gaap_CommonClassAMember_019c9670-f331-7b4a-a1c8-5ab12318c2c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019c9670-f331-719c-80aa-f47a43ef256f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7000-8826-276ca1253a37" xlink:to="loc_us-gaap_CommonClassBMember_019c9670-f331-719c-80aa-f47a43ef256f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassVMember_019c9670-f331-713b-8ea2-f05a7336e32e" xlink:href="alit-20260331.xsd#alit_CommonClassVMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7000-8826-276ca1253a37" xlink:to="loc_alit_CommonClassVMember_019c9670-f331-713b-8ea2-f05a7336e32e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassZMember_019c9670-f331-713a-8a24-c16b3f4fc12a" xlink:href="alit-20260331.xsd#alit_CommonClassZMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7000-8826-276ca1253a37" xlink:to="loc_alit_CommonClassZMember_019c9670-f331-713a-8a24-c16b3f4fc12a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7f11-9339-6741169d45a7" xlink:to="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019c9670-f331-7b6e-867b-644ada12522f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019c9670-f331-7b6e-867b-644ada12522f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019c9670-f331-749f-9e0d-78c12d8417aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c9670-f331-7b6e-867b-644ada12522f" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019c9670-f331-749f-9e0d-78c12d8417aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019c9670-f331-7100-85eb-85df798d0aad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c9670-f331-7b6e-867b-644ada12522f" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019c9670-f331-7100-85eb-85df798d0aad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_019c9670-f331-7591-94e9-52530741abd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c9670-f331-7b6e-867b-644ada12522f" xlink:to="loc_us-gaap_OtherAssetsCurrent_019c9670-f331-7591-94e9-52530741abd3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_FiduciaryAssetsCurrent_019c9670-f331-716c-b2e0-3b8290931a95" xlink:href="alit-20260331.xsd#alit_FiduciaryAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c9670-f331-7b6e-867b-644ada12522f" xlink:to="loc_alit_FiduciaryAssetsCurrent_019c9670-f331-716c-b2e0-3b8290931a95" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019c9670-f331-7940-9c5b-42198d7fc806" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c9670-f331-7b6e-867b-644ada12522f" xlink:to="loc_us-gaap_AssetsCurrent_019c9670-f331-7940-9c5b-42198d7fc806" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019c9670-f331-799d-8890-57deb52c1b4f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:to="loc_us-gaap_Goodwill_019c9670-f331-799d-8890-57deb52c1b4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019c9670-f331-7983-98fa-9151afff97a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019c9670-f331-7983-98fa-9151afff97a2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_019c9670-f331-7e29-b263-b3cc88cec307" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_019c9670-f331-7e29-b263-b3cc88cec307" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_019c9670-f331-7d68-b67a-59a6f38815dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_019c9670-f331-7d68-b67a-59a6f38815dc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019c9670-f331-784e-bc63-b8f7310151c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019c9670-f331-784e-bc63-b8f7310151c0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019c9670-f331-7fd9-9934-bf30b38c4dfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c9670-f331-76eb-b168-eb83c9736cde" xlink:to="loc_us-gaap_Assets_019c9670-f331-7fd9-9934-bf30b38c4dfa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c9670-f331-785b-980b-a1996bcd38c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7f11-9339-6741169d45a7" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c9670-f331-785b-980b-a1996bcd38c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_019c9670-f331-7269-8040-cbf75f2e57d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c9670-f331-785b-980b-a1996bcd38c6" xlink:to="loc_us-gaap_LiabilitiesAbstract_019c9670-f331-7269-8040-cbf75f2e57d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019c9670-f331-7be2-9a0d-e115f4e12e7a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c9670-f331-7269-8040-cbf75f2e57d1" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019c9670-f331-7be2-9a0d-e115f4e12e7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019c9670-f331-70d6-86ef-e4503c5140e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c9670-f331-7be2-9a0d-e115f4e12e7a" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019c9670-f331-70d6-86ef-e4503c5140e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019c9670-f331-72b1-bfa9-57fea387406b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c9670-f331-7be2-9a0d-e115f4e12e7a" xlink:to="loc_us-gaap_LongTermDebtCurrent_019c9670-f331-72b1-bfa9-57fea387406b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_019c9670-f331-7a86-a8c2-a8d1ceb985bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c9670-f331-7be2-9a0d-e115f4e12e7a" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_019c9670-f331-7a86-a8c2-a8d1ceb985bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_FiduciaryLiabilitiesCurrent_019c9670-f331-7bfb-be8a-d0e8c8f0a89c" xlink:href="alit-20260331.xsd#alit_FiduciaryLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c9670-f331-7be2-9a0d-e115f4e12e7a" xlink:to="loc_alit_FiduciaryLiabilitiesCurrent_019c9670-f331-7bfb-be8a-d0e8c8f0a89c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019c9670-f331-7730-85a8-8ca5d812b15d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c9670-f331-7be2-9a0d-e115f4e12e7a" xlink:to="loc_us-gaap_LiabilitiesCurrent_019c9670-f331-7730-85a8-8ca5d812b15d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019c9670-f331-7866-85d8-6fa2c787bae9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c9670-f331-7269-8040-cbf75f2e57d1" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019c9670-f331-7866-85d8-6fa2c787bae9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019c9670-f331-76a8-81b8-c475c207eae8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c9670-f331-7269-8040-cbf75f2e57d1" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019c9670-f331-76a8-81b8-c475c207eae8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementObligationsNoncurrent_019c9670-f331-734c-9845-847986656794" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementObligationsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c9670-f331-7269-8040-cbf75f2e57d1" xlink:to="loc_alit_TaxReceivableAgreementObligationsNoncurrent_019c9670-f331-734c-9845-847986656794" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019c9670-f331-753d-992d-3bf37e6e26f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c9670-f331-7269-8040-cbf75f2e57d1" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019c9670-f331-753d-992d-3bf37e6e26f3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019c9670-f331-7eda-ac9c-a6463c808a64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c9670-f331-7269-8040-cbf75f2e57d1" xlink:to="loc_us-gaap_Liabilities_019c9670-f331-7eda-ac9c-a6463c808a64" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019c9670-f331-7b42-af66-e17c8bc044d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c9670-f331-785b-980b-a1996bcd38c6" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019c9670-f331-7b42-af66-e17c8bc044d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c9670-f331-785b-980b-a1996bcd38c6" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_019c9670-f331-7d0d-824d-193a98b20568" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_PreferredStockValue_019c9670-f331-7d0d-824d-193a98b20568" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019c9670-f331-7222-8b43-070fa3210c9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_CommonStockValue_019c9670-f331-7222-8b43-070fa3210c9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonValue_019c9670-f331-754d-a052-af6143dfb399" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_TreasuryStockCommonValue_019c9670-f331-754d-a052-af6143dfb399" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_019c9670-f331-7b0d-bd8e-b1edac4675a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_AdditionalPaidInCapital_019c9670-f331-7b0d-bd8e-b1edac4675a5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019c9670-f331-76cf-9b7d-5eb75d7df45f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019c9670-f331-76cf-9b7d-5eb75d7df45f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019c9670-f331-7a8b-82a7-2551dd9f0de3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019c9670-f331-7a8b-82a7-2551dd9f0de3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019c9670-f331-7c94-b30c-79feb6ab8787" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_StockholdersEquity_019c9670-f331-7c94-b30c-79feb6ab8787" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019c9670-f331-7445-a6e1-cd8bf7f05056" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_MinorityInterest_019c9670-f331-7445-a6e1-cd8bf7f05056" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c9670-f331-7e73-a740-4da5a890a195" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c9670-f331-7f47-b902-e21e77d2ed0f" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c9670-f331-7e73-a740-4da5a890a195" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019c9670-f331-7550-863f-b50748de5f3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c9670-f331-785b-980b-a1996bcd38c6" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019c9670-f331-7550-863f-b50748de5f3a" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="alit-20260331.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://alight.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019c9670-f331-7fa4-9c49-399ebd5660bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_StatementTable_019c9670-f331-7fa4-9c49-399ebd5660bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019c9670-f331-72f7-bfb4-5dbbad6b90fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019c9670-f331-7fa4-9c49-399ebd5660bf" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019c9670-f331-72f7-bfb4-5dbbad6b90fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f331-72f7-bfb4-5dbbad6b90fd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f331-72f7-bfb4-5dbbad6b90fd" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f331-72f7-bfb4-5dbbad6b90fd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7e5e-a2cd-a8fba799b568" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f331-72f7-bfb4-5dbbad6b90fd" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7e5e-a2cd-a8fba799b568" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019c9670-f331-77ae-b1b9-4b159341b9cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7e5e-a2cd-a8fba799b568" xlink:to="loc_us-gaap_CommonClassAMember_019c9670-f331-77ae-b1b9-4b159341b9cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019c9670-f331-71a7-b2b1-0f9f829eb896" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7e5e-a2cd-a8fba799b568" xlink:to="loc_us-gaap_CommonClassBMember_019c9670-f331-71a7-b2b1-0f9f829eb896" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassVMember_019c9670-f331-7a65-8075-b78968f3a253" xlink:href="alit-20260331.xsd#alit_CommonClassVMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7e5e-a2cd-a8fba799b568" xlink:to="loc_alit_CommonClassVMember_019c9670-f331-7a65-8075-b78968f3a253" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassZMember_019c9670-f331-7d76-a6c6-8567ed64c51b" xlink:href="alit-20260331.xsd#alit_CommonClassZMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f331-7e5e-a2cd-a8fba799b568" xlink:to="loc_alit_CommonClassZMember_019c9670-f331-7d76-a6c6-8567ed64c51b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019c9670-f331-7787-9aba-eae65460a7dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019c9670-f331-7787-9aba-eae65460a7dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019c9670-f331-70c7-a3ad-83ab1fc75d59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019c9670-f331-70c7-a3ad-83ab1fc75d59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019c9670-f331-70f9-9718-8e38c0af726b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019c9670-f331-70f9-9718-8e38c0af726b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019c9670-f331-7330-85c6-79c11afb6474" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019c9670-f331-7330-85c6-79c11afb6474" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019c9670-f331-7b5c-9e84-0414aca8e99a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019c9670-f331-7b5c-9e84-0414aca8e99a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019c9670-f331-73bb-aef9-ee91944aac6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019c9670-f331-73bb-aef9-ee91944aac6c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019c9670-f331-7f09-96a2-e1a4781981e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_CommonStockSharesIssued_019c9670-f331-7f09-96a2-e1a4781981e5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019c9670-f331-7b87-a00a-a9f70e20d732" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019c9670-f331-7b87-a00a-a9f70e20d732" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019c9670-f331-7dea-999a-0a62899a8164" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7bc4-a9fc-23cdd59488ed" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019c9670-f331-7dea-999a-0a62899a8164" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="alit-20260331.xsd#CondensedConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://alight.com/role/CondensedConsolidatedStatementsofStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019c9670-f331-7cd6-8ed5-a35831a33c9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019c9670-f331-70c3-9963-dc371a73bfce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7cd6-8ed5-a35831a33c9f" xlink:to="loc_us-gaap_StatementTable_019c9670-f331-70c3-9963-dc371a73bfce" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f331-7c64-8d8e-bbb2fc0693f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019c9670-f331-70c3-9963-dc371a73bfce" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f331-7c64-8d8e-bbb2fc0693f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9670-f331-7c64-8d8e-bbb2fc0693f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f331-7c64-8d8e-bbb2fc0693f1" xlink:to="loc_us-gaap_EquityComponentDomain_019c9670-f331-7c64-8d8e-bbb2fc0693f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9670-f331-78d4-9b67-0939cb892914" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f331-7c64-8d8e-bbb2fc0693f1" xlink:to="loc_us-gaap_EquityComponentDomain_019c9670-f331-78d4-9b67-0939cb892914" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_019c9670-f331-7843-8896-bcbd65528b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c9670-f331-78d4-9b67-0939cb892914" xlink:to="loc_us-gaap_ParentMember_019c9670-f331-7843-8896-bcbd65528b9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019c9670-f331-7d25-82b9-eebca3c99810" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c9670-f331-7843-8896-bcbd65528b9e" xlink:to="loc_us-gaap_CommonStockMember_019c9670-f331-7d25-82b9-eebca3c99810" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019c9670-f331-7533-8dc4-4c86edcb1eda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c9670-f331-7843-8896-bcbd65528b9e" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019c9670-f331-7533-8dc4-4c86edcb1eda" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019c9670-f331-79ad-8a92-7d8e564eb4e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c9670-f331-7843-8896-bcbd65528b9e" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019c9670-f331-79ad-8a92-7d8e564eb4e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019c9670-f331-79e5-8a95-48c56724b35c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c9670-f331-7843-8896-bcbd65528b9e" xlink:to="loc_us-gaap_RetainedEarningsMember_019c9670-f331-79e5-8a95-48c56724b35c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019c9670-f331-75ca-983b-714691e8edeb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c9670-f331-7843-8896-bcbd65528b9e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019c9670-f331-75ca-983b-714691e8edeb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019c9670-f331-7765-b792-3f30a584a658" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c9670-f331-78d4-9b67-0939cb892914" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019c9670-f331-7765-b792-3f30a584a658" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c9670-f331-7cd6-8ed5-a35831a33c9f" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c9670-f331-7ad3-bdd3-a062d577faa6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c9670-f331-7ad3-bdd3-a062d577faa6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019c9670-f331-7312-a334-0c052c8d4a36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:to="loc_us-gaap_ProfitLoss_019c9670-f331-7312-a334-0c052c8d4a36" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019c9670-f331-70a1-827c-7ec724ae5fd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019c9670-f331-70a1-827c-7ec724ae5fd9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019c9670-f331-7e4f-9d2a-a1d595cac205" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019c9670-f331-7e4f-9d2a-a1d595cac205" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SharesWithheldInLieuOfTaxes_019c9670-f331-74c8-967e-fe0ca467dbe0" xlink:href="alit-20260331.xsd#alit_SharesWithheldInLieuOfTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:to="loc_alit_SharesWithheldInLieuOfTaxes_019c9670-f331-74c8-967e-fe0ca467dbe0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockRetiredCostMethodAmount_019c9670-f331-7f0a-a851-2b988c22bbe7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockRetiredCostMethodAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:to="loc_us-gaap_TreasuryStockRetiredCostMethodAmount_019c9670-f331-7f0a-a851-2b988c22bbe7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_019c9670-f331-7146-bc15-445e0925e47c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_019c9670-f331-7146-bc15-445e0925e47c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueOther_019c9670-f331-7b78-afba-101dde833bc0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f331-7024-b880-5725f59d824c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueOther_019c9670-f331-7b78-afba-101dde833bc0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c9670-f331-7087-aa8e-39b212a8e695" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/BasisofPresentationandNatureofBusinessAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#BasisofPresentationandNatureofBusinessAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/BasisofPresentationandNatureofBusinessAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_alit_BasisOfPresentationAndNatureOfBusinessLineItems_019c9670-f331-7a53-b684-9c505350869e" xlink:href="alit-20260331.xsd#alit_BasisOfPresentationAndNatureOfBusinessLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_BasisOfPresentationAndNatureOfBusinessTable_019c9670-f331-7b6b-8abd-6c6e6660747b" xlink:href="alit-20260331.xsd#alit_BasisOfPresentationAndNatureOfBusinessTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_alit_BasisOfPresentationAndNatureOfBusinessLineItems_019c9670-f331-7a53-b684-9c505350869e" xlink:to="loc_alit_BasisOfPresentationAndNatureOfBusinessTable_019c9670-f331-7b6b-8abd-6c6e6660747b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019c9670-f331-71e1-8204-0ded6cae24a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_BasisOfPresentationAndNatureOfBusinessTable_019c9670-f331-7b6b-8abd-6c6e6660747b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019c9670-f331-71e1-8204-0ded6cae24a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019c9670-f331-71e1-8204-0ded6cae24a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019c9670-f331-71e1-8204-0ded6cae24a6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019c9670-f331-71e1-8204-0ded6cae24a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019c9670-f331-72b9-8f1e-19b97ca8f404" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019c9670-f331-71e1-8204-0ded6cae24a6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019c9670-f331-72b9-8f1e-19b97ca8f404" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SpecialPurposeAcquisitionCompanyMember_019c9670-f331-7bbc-92b8-51265a39815c" xlink:href="alit-20260331.xsd#alit_SpecialPurposeAcquisitionCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019c9670-f331-72b9-8f1e-19b97ca8f404" xlink:to="loc_alit_SpecialPurposeAcquisitionCompanyMember_019c9670-f331-7bbc-92b8-51265a39815c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019c9670-f331-75ba-9a7d-0ed8c437a9c0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_BasisOfPresentationAndNatureOfBusinessTable_019c9670-f331-7b6b-8abd-6c6e6660747b" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019c9670-f331-75ba-9a7d-0ed8c437a9c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c9670-f331-75ba-9a7d-0ed8c437a9c0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c9670-f331-75ba-9a7d-0ed8c437a9c0" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c9670-f331-75ba-9a7d-0ed8c437a9c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c9670-f331-72b4-a45b-eae673583c59" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c9670-f331-75ba-9a7d-0ed8c437a9c0" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c9670-f331-72b4-a45b-eae673583c59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AlightGroupIncMember_019c9670-f331-720d-8a8f-0819bf432d0d" xlink:href="alit-20260331.xsd#alit_AlightGroupIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019c9670-f331-72b4-a45b-eae673583c59" xlink:to="loc_alit_AlightGroupIncMember_019c9670-f331-720d-8a8f-0819bf432d0d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019c9670-f331-77f0-aea0-e266bd0c4baf" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_BasisOfPresentationAndNatureOfBusinessTable_019c9670-f331-7b6b-8abd-6c6e6660747b" xlink:to="loc_srt_OwnershipAxis_019c9670-f331-77f0-aea0-e266bd0c4baf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019c9670-f331-77f0-aea0-e266bd0c4baf_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019c9670-f331-77f0-aea0-e266bd0c4baf" xlink:to="loc_srt_OwnershipDomain_019c9670-f331-77f0-aea0-e266bd0c4baf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019c9670-f331-7b8d-b55c-977320c7ef89" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019c9670-f331-77f0-aea0-e266bd0c4baf" xlink:to="loc_srt_OwnershipDomain_019c9670-f331-7b8d-b55c-977320c7ef89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AlightHoldingsMember_019c9670-f331-7180-bc00-533343c48c4a" xlink:href="alit-20260331.xsd#alit_AlightHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019c9670-f331-7b8d-b55c-977320c7ef89" xlink:to="loc_alit_AlightHoldingsMember_019c9670-f331-7180-bc00-533343c48c4a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c9670-f331-76c0-9636-8d687890e108" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_BasisOfPresentationAndNatureOfBusinessTable_019c9670-f331-7b6b-8abd-6c6e6660747b" xlink:to="loc_srt_RangeAxis_019c9670-f331-76c0-9636-8d687890e108" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c9670-f331-76c0-9636-8d687890e108_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c9670-f331-76c0-9636-8d687890e108" xlink:to="loc_srt_RangeMember_019c9670-f331-76c0-9636-8d687890e108_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c9670-f331-7200-ae5c-f1f5ca5464d3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c9670-f331-76c0-9636-8d687890e108" xlink:to="loc_srt_RangeMember_019c9670-f331-7200-ae5c-f1f5ca5464d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c9670-f331-78f5-9747-097cd350881a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c9670-f331-7200-ae5c-f1f5ca5464d3" xlink:to="loc_srt_MaximumMember_019c9670-f331-78f5-9747-097cd350881a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019c9670-f331-78a6-afc8-b362885a358c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_BasisOfPresentationAndNatureOfBusinessLineItems_019c9670-f331-7a53-b684-9c505350869e" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_019c9670-f331-78a6-afc8-b362885a358c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019c9670-f331-7a35-84b0-985abbdb6e61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_BasisOfPresentationAndNatureOfBusinessLineItems_019c9670-f331-7a53-b684-9c505350869e" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019c9670-f331-7a35-84b0-985abbdb6e61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_019c9670-f331-72c6-bd8d-42ea558a7878" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_BasisOfPresentationAndNatureOfBusinessLineItems_019c9670-f331-7a53-b684-9c505350869e" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_019c9670-f331-72c6-bd8d-42ea558a7878" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/RevenuefromContractswithCustomersAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#RevenuefromContractswithCustomersAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/RevenuefromContractswithCustomersAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019c9670-f331-7851-bb41-32a1b13bc00e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019c9670-f331-7fa7-8796-511ee38bb965" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c9670-f331-7851-bb41-32a1b13bc00e" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019c9670-f331-7fa7-8796-511ee38bb965" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c9670-f331-7c47-84ff-2d6269a936d3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c9670-f331-7fa7-8796-511ee38bb965" xlink:to="loc_srt_RangeAxis_019c9670-f331-7c47-84ff-2d6269a936d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c9670-f331-7c47-84ff-2d6269a936d3_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c9670-f331-7c47-84ff-2d6269a936d3" xlink:to="loc_srt_RangeMember_019c9670-f331-7c47-84ff-2d6269a936d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c9670-f331-74d2-a295-2b711213174b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c9670-f331-7c47-84ff-2d6269a936d3" xlink:to="loc_srt_RangeMember_019c9670-f331-74d2-a295-2b711213174b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019c9670-f331-7bb9-87e9-2a14cd1c06dc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c9670-f331-74d2-a295-2b711213174b" xlink:to="loc_srt_MinimumMember_019c9670-f331-7bb9-87e9-2a14cd1c06dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c9670-f331-7e1a-b7db-ff41c7053cfc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c9670-f331-74d2-a295-2b711213174b" xlink:to="loc_srt_MaximumMember_019c9670-f331-7e1a-b7db-ff41c7053cfc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f331-7252-b90f-27ef868a7eb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c9670-f331-7fa7-8796-511ee38bb965" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f331-7252-b90f-27ef868a7eb7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f331-7252-b90f-27ef868a7eb7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f331-7252-b90f-27ef868a7eb7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f331-7252-b90f-27ef868a7eb7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f331-75a7-b540-89847436c6f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f331-7252-b90f-27ef868a7eb7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f331-75a7-b540-89847436c6f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019c9670-f331-73ab-8cdc-448821b7d69d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f331-75a7-b540-89847436c6f7" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019c9670-f331-73ab-8cdc-448821b7d69d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019c9670-f331-711b-bd98-1b0b9a72d08a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c9670-f331-7fa7-8796-511ee38bb965" xlink:to="loc_srt_ProductOrServiceAxis_019c9670-f331-711b-bd98-1b0b9a72d08a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019c9670-f331-711b-bd98-1b0b9a72d08a_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019c9670-f331-711b-bd98-1b0b9a72d08a" xlink:to="loc_srt_ProductsAndServicesDomain_019c9670-f331-711b-bd98-1b0b9a72d08a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019c9670-f331-743d-ae1b-786b53d6855f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019c9670-f331-711b-bd98-1b0b9a72d08a" xlink:to="loc_srt_ProductsAndServicesDomain_019c9670-f331-743d-ae1b-786b53d6855f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_OtherSolutionsMember_019c9670-f331-7a90-a0e4-44c27a2475ca" xlink:href="alit-20260331.xsd#alit_OtherSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c9670-f331-743d-ae1b-786b53d6855f" xlink:to="loc_alit_OtherSolutionsMember_019c9670-f331-7a90-a0e4-44c27a2475ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PayrollAndCloudLeavesSolutionsMember_019c9670-f331-711b-91ae-8b000bcededf" xlink:href="alit-20260331.xsd#alit_PayrollAndCloudLeavesSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c9670-f331-743d-ae1b-786b53d6855f" xlink:to="loc_alit_PayrollAndCloudLeavesSolutionsMember_019c9670-f331-711b-91ae-8b000bcededf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAxis_019c9670-f331-7123-a444-185c4961dac6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c9670-f331-7fa7-8796-511ee38bb965" xlink:to="loc_us-gaap_CapitalizedContractCostAxis_019c9670-f331-7123-a444-185c4961dac6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_019c9670-f331-7123-a444-185c4961dac6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_019c9670-f331-7123-a444-185c4961dac6" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_019c9670-f331-7123-a444-185c4961dac6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_019c9670-f331-7259-a0f8-39e5be8f9ef3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_019c9670-f331-7123-a444-185c4961dac6" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_019c9670-f331-7259-a0f8-39e5be8f9ef3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CostsToObtainAContractMember_019c9670-f331-789d-a585-0d683bfa3c60" xlink:href="alit-20260331.xsd#alit_CostsToObtainAContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_019c9670-f331-7259-a0f8-39e5be8f9ef3" xlink:to="loc_alit_CostsToObtainAContractMember_019c9670-f331-789d-a585-0d683bfa3c60" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CostsToFulfillAContractMember_019c9670-f331-78ac-9382-7152205bf23f" xlink:href="alit-20260331.xsd#alit_CostsToFulfillAContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_019c9670-f331-7259-a0f8-39e5be8f9ef3" xlink:to="loc_alit_CostsToFulfillAContractMember_019c9670-f331-78ac-9382-7152205bf23f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AdministrationServicesContractTerm_019c9670-f331-7a8d-bd03-3be31d3a23c6" xlink:href="alit-20260331.xsd#alit_AdministrationServicesContractTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c9670-f331-7851-bb41-32a1b13bc00e" xlink:to="loc_alit_AdministrationServicesContractTerm_019c9670-f331-7a8d-bd03-3be31d3a23c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_HealthSolutionsAdministrationServicesContractTerm_019c9670-f331-7c88-9b92-60487ca18faa" xlink:href="alit-20260331.xsd#alit_HealthSolutionsAdministrationServicesContractTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c9670-f331-7851-bb41-32a1b13bc00e" xlink:to="loc_alit_HealthSolutionsAdministrationServicesContractTerm_019c9670-f331-7c88-9b92-60487ca18faa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PeriodToRecognizeRevenueUnderSubscription_019c9670-f331-749a-9225-b8906925b114" xlink:href="alit-20260331.xsd#alit_PeriodToRecognizeRevenueUnderSubscription"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c9670-f331-7851-bb41-32a1b13bc00e" xlink:to="loc_alit_PeriodToRecognizeRevenueUnderSubscription_019c9670-f331-749a-9225-b8906925b114" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_019c9670-f331-72e5-9f6b-d3508088f432" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c9670-f331-7851-bb41-32a1b13bc00e" xlink:to="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_019c9670-f331-72e5-9f6b-d3508088f432" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/DiscontinuedOperationsAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#DiscontinuedOperationsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/DiscontinuedOperationsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-74d4-bc03-85a6671f3f5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-74d4-bc03-85a6671f3f5d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019db17b-a96f-7405-922d-50314f7826bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-74d4-bc03-85a6671f3f5d" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019db17b-a96f-7405-922d-50314f7826bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019db17b-a96f-7405-922d-50314f7826bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019db17b-a96f-7405-922d-50314f7826bc" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019db17b-a96f-7405-922d-50314f7826bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019db17b-a96f-700b-8a1c-1a009ecc007c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019db17b-a96f-7405-922d-50314f7826bc" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019db17b-a96f-700b-8a1c-1a009ecc007c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019db17b-a96f-7e76-a09e-4562dcd07926" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019db17b-a96f-700b-8a1c-1a009ecc007c" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019db17b-a96f-7e76-a09e-4562dcd07926" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019db17b-a96f-76d5-9248-2350008a1917" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-74d4-bc03-85a6671f3f5d" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019db17b-a96f-76d5-9248-2350008a1917" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019db17b-a96f-76d5-9248-2350008a1917_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019db17b-a96f-76d5-9248-2350008a1917" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019db17b-a96f-76d5-9248-2350008a1917_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019db17b-a96f-73ec-8db2-8e5aea3d70c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019db17b-a96f-76d5-9248-2350008a1917" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019db17b-a96f-73ec-8db2-8e5aea3d70c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DivestedBusinessMember_019db17b-a96f-7fdb-b84d-07d2004f90e5" xlink:href="alit-20260331.xsd#alit_DivestedBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019db17b-a96f-73ec-8db2-8e5aea3d70c6" xlink:to="loc_alit_DivestedBusinessMember_019db17b-a96f-7fdb-b84d-07d2004f90e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019db17b-a96f-7411-aa48-a845daec46a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-74d4-bc03-85a6671f3f5d" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019db17b-a96f-7411-aa48-a845daec46a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019db17b-a96f-7411-aa48-a845daec46a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019db17b-a96f-7411-aa48-a845daec46a6" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019db17b-a96f-7411-aa48-a845daec46a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019db1a8-cb89-7f3b-a3d9-4c9cf11a4f0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019db17b-a96f-7411-aa48-a845daec46a6" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019db1a8-cb89-7f3b-a3d9-4c9cf11a4f0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019db17b-a96f-77ed-8641-f21aaeda3059" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019db1a8-cb89-7f3b-a3d9-4c9cf11a4f0b" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019db17b-a96f-77ed-8641-f21aaeda3059" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019db17b-a96f-72bc-9824-2ca831357280" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019db17b-a96f-77ed-8641-f21aaeda3059" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019db17b-a96f-72bc-9824-2ca831357280" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019db17b-a96f-7223-bd5f-6fe3f5476164" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-74d4-bc03-85a6671f3f5d" xlink:to="loc_srt_ProductOrServiceAxis_019db17b-a96f-7223-bd5f-6fe3f5476164" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019db17b-a96f-7223-bd5f-6fe3f5476164_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019db17b-a96f-7223-bd5f-6fe3f5476164" xlink:to="loc_srt_ProductsAndServicesDomain_019db17b-a96f-7223-bd5f-6fe3f5476164_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019db17b-a96f-7be2-ae44-a45eb92575b5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019db17b-a96f-7223-bd5f-6fe3f5476164" xlink:to="loc_srt_ProductsAndServicesDomain_019db17b-a96f-7be2-ae44-a45eb92575b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CustomerCareCommercialServicesMember_019db17b-a96f-7d1c-90fb-efdff81c399e" xlink:href="alit-20260331.xsd#alit_CustomerCareCommercialServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019db17b-a96f-7be2-ae44-a45eb92575b5" xlink:to="loc_alit_CustomerCareCommercialServicesMember_019db17b-a96f-7d1c-90fb-efdff81c399e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CloudServicesSegmentsMember_019db17b-cfb3-7c97-859c-75ec8782ad9a" xlink:href="alit-20260331.xsd#alit_CloudServicesSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019db17b-a96f-7be2-ae44-a45eb92575b5" xlink:to="loc_alit_CloudServicesSegmentsMember_019db17b-cfb3-7c97-859c-75ec8782ad9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_019db17b-a96f-7e2e-8352-459d3cf39645" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_019db17b-a96f-7e2e-8352-459d3cf39645" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_019db17b-a96f-7629-83d6-41e665af8725" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_019db17b-a96f-7629-83d6-41e665af8725" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmount_019db17b-a96f-7470-85ee-088ee2183fbd" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmount_019db17b-a96f-7470-85ee-088ee2183fbd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmountFairValue_019db17b-a96f-704b-853e-258fb76296ac" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmountFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmountFairValue_019db17b-a96f-704b-853e-258fb76296ac" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmount_019db17b-a96f-7a65-8dc9-c464540a5c6c" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmount_019db17b-a96f-7a65-8dc9-c464540a5c6c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmountFairValue_019db17b-a96f-7d35-8909-8f9a42474615" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmountFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmountFairValue_019db17b-a96f-7d35-8909-8f9a42474615" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationStatedInterestRate_019db17b-a96f-7dca-ae4c-71ac1fbd91d6" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationConsiderationStatedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationStatedInterestRate_019db17b-a96f-7dca-ae4c-71ac1fbd91d6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationTransitionServicesAgreementInitialPeriod_019db17b-a96f-76dc-a794-5125998331a1" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationTransitionServicesAgreementInitialPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationTransitionServicesAgreementInitialPeriod_019db17b-a96f-76dc-a794-5125998331a1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationTransitionServicesAgreementOptionToExtend_019db17b-a96f-71c3-872d-6a3667419b92" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationTransitionServicesAgreementOptionToExtend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationTransitionServicesAgreementOptionToExtend_019db17b-a96f-71c3-872d-6a3667419b92" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationTransitionServicesAgreementIncome_019db17b-a96f-741d-80ed-9060fddd105a" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationConsiderationTransitionServicesAgreementIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationTransitionServicesAgreementIncome_019db17b-a96f-741d-80ed-9060fddd105a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationTransitionServicesAgreementPassThroughCosts_019db17b-a96f-7e89-81aa-ddae7da680a3" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationConsiderationTransitionServicesAgreementPassThroughCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationTransitionServicesAgreementPassThroughCosts_019db17b-a96f-7e89-81aa-ddae7da680a3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019db17b-a96f-7ab8-aced-29a4906d21e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019db17b-a96f-7ab8-aced-29a4906d21e8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_019db17b-cfb3-7d3b-9049-99a590f528bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019db17b-a96f-7be4-89b0-0dd1034ca6a8" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_019db17b-cfb3-7d3b-9049-99a590f528bd" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/DiscontinuedOperationsSummaryofIncomelossfromDiscontinuedOperationsonCondensedConsolidatedStatementsofComprehensiveIncomelossDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#DiscontinuedOperationsSummaryofIncomelossfromDiscontinuedOperationsonCondensedConsolidatedStatementsofComprehensiveIncomelossDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/DiscontinuedOperationsSummaryofIncomelossfromDiscontinuedOperationsonCondensedConsolidatedStatementsofComprehensiveIncomelossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-71d6-a644-f5eae91c272a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-71d6-a644-f5eae91c272a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019c9670-f331-7ea7-bf7f-66104fca02fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-71d6-a644-f5eae91c272a" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019c9670-f331-7ea7-bf7f-66104fca02fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f331-7ea7-bf7f-66104fca02fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019c9670-f331-7ea7-bf7f-66104fca02fc" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f331-7ea7-bf7f-66104fca02fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f331-7af8-96e6-62d6be34d205" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019c9670-f331-7ea7-bf7f-66104fca02fc" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f331-7af8-96e6-62d6be34d205" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DivestedBusinessMember_019c9670-f331-7335-90c1-e3ad12898547" xlink:href="alit-20260331.xsd#alit_DivestedBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f331-7af8-96e6-62d6be34d205" xlink:to="loc_alit_DivestedBusinessMember_019c9670-f331-7335-90c1-e3ad12898547" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019c9670-f331-7c10-85b3-0475f5b1758a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019c9670-f331-71d6-a644-f5eae91c272a" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019c9670-f331-7c10-85b3-0475f5b1758a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f331-7c10-85b3-0475f5b1758a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019c9670-f331-7c10-85b3-0475f5b1758a" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f331-7c10-85b3-0475f5b1758a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f331-7a9a-ba84-d1b1b5a3e51b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019c9670-f331-7c10-85b3-0475f5b1758a" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f331-7a9a-ba84-d1b1b5a3e51b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019c9670-f331-7ab7-abc0-85d4f48a5b54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f331-7a9a-ba84-d1b1b5a3e51b" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019c9670-f331-7ab7-abc0-85d4f48a5b54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019c9670-f331-751f-9dcd-34fcdf6bb664" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_019c9670-f331-751f-9dcd-34fcdf6bb664" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_019c9670-f331-7092-a518-c0b2e785fea8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_019c9670-f331-7092-a518-c0b2e785fea8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortizationBeforeGrossProfit_019c9670-f331-7609-bc2a-49e91a0e68ee" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortizationBeforeGrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortizationBeforeGrossProfit_019c9670-f331-7609-bc2a-49e91a0e68ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss_019c9670-f331-70bc-bb59-2f77a3d90612" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGrossProfitLoss_019c9670-f331-70bc-bb59-2f77a3d90612" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019c9670-f331-7e7a-a44d-f64e2b90b36b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019c9670-f331-7e7a-a44d-f64e2b90b36b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense_019c9670-f331-7a53-b6c0-b838d31df66a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019c9670-f331-7e7a-a44d-f64e2b90b36b" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense_019c9670-f331-7a53-b6c0-b838d31df66a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_019c9670-f331-7984-a1ef-3142f4dd64f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019c9670-f331-7e7a-a44d-f64e2b90b36b" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_019c9670-f331-7984-a1ef-3142f4dd64f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense_019c9670-f331-71c1-928a-e80a6daaa771" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019c9670-f331-7e7a-a44d-f64e2b90b36b" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense_019c9670-f331-71c1-928a-e80a6daaa771" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_019c9670-f331-784c-88e6-52bb4ff407b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_019c9670-f331-784c-88e6-52bb4ff407b7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseNet_019c9670-f331-7136-8430-175762d86f3d" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseNet_019c9670-f331-7136-8430-175762d86f3d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019c9670-f331-78af-8162-d979f9b27492" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_019c9670-f331-78af-8162-d979f9b27492" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_019c9670-f331-7ff5-972d-ca4a7ae0f198" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_019c9670-f331-7ff5-972d-ca4a7ae0f198" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_019c9670-f331-761e-ace9-7ebb3834f16b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_019c9670-f331-761e-ace9-7ebb3834f16b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019c9670-f331-7b6a-9e68-a4678f0642ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019c9670-f331-7146-8a35-873cbe270563" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_019c9670-f331-7b6a-9e68-a4678f0642ae" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/OtherFinancialDataAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#OtherFinancialDataAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/OtherFinancialDataAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:href="alit-20260331.xsd#alit_OtherFinancialDataLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_OtherFinancialDataTable_019c9670-f3e3-7f29-a819-55dac1e72989" xlink:href="alit-20260331.xsd#alit_OtherFinancialDataTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:to="loc_alit_OtherFinancialDataTable_019c9670-f3e3-7f29-a819-55dac1e72989" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019c9670-f3e3-727e-91af-1d400e23119b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_OtherFinancialDataTable_019c9670-f3e3-7f29-a819-55dac1e72989" xlink:to="loc_srt_ProductOrServiceAxis_019c9670-f3e3-727e-91af-1d400e23119b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019c9670-f3e3-727e-91af-1d400e23119b_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019c9670-f3e3-727e-91af-1d400e23119b" xlink:to="loc_srt_ProductsAndServicesDomain_019c9670-f3e3-727e-91af-1d400e23119b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019c9670-f3e3-7e3c-8c06-9b08d859ab21" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019c9670-f3e3-727e-91af-1d400e23119b" xlink:to="loc_srt_ProductsAndServicesDomain_019c9670-f3e3-7e3c-8c06-9b08d859ab21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_019c9670-f3e3-7da7-9cef-e5fc645fe993" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c9670-f3e3-7e3c-8c06-9b08d859ab21" xlink:to="loc_us-gaap_ServiceMember_019c9670-f3e3-7da7-9cef-e5fc645fe993" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c9670-f3e3-7806-9aff-e678b6321eb0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_OtherFinancialDataTable_019c9670-f3e3-7f29-a819-55dac1e72989" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c9670-f3e3-7806-9aff-e678b6321eb0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e3-7806-9aff-e678b6321eb0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c9670-f3e3-7806-9aff-e678b6321eb0" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e3-7806-9aff-e678b6321eb0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e3-77b8-a468-a87acd6a5e01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c9670-f3e3-7806-9aff-e678b6321eb0" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e3-77b8-a468-a87acd6a5e01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019c9670-f3e3-72f9-ba83-a0b01748f3f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e3-77b8-a468-a87acd6a5e01" xlink:to="loc_us-gaap_InterestRateSwapMember_019c9670-f3e3-72f9-ba83-a0b01748f3f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortization_019c9670-f3e3-72fc-92fb-4a9507fb78a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:to="loc_us-gaap_CapitalizedContractCostAmortization_019c9670-f3e3-72fc-92fb-4a9507fb78a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_019c9670-f3e3-700f-86f6-6893ab37c9fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_019c9670-f3e3-700f-86f6-6893ab37c9fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsNoncurrent_019c9670-f3e3-72d0-9e08-8db7423bd09e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:to="loc_us-gaap_DerivativeAssetsNoncurrent_019c9670-f3e3-72d0-9e08-8db7423bd09e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_OtherAssetsConsiderationReceivableSellerNote_019c9670-f3e3-7921-9fc9-518260400372" xlink:href="alit-20260331.xsd#alit_OtherAssetsConsiderationReceivableSellerNote"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:to="loc_alit_OtherAssetsConsiderationReceivableSellerNote_019c9670-f3e3-7921-9fc9-518260400372" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019c9670-f3e3-7300-8bf5-fb4cdd3f0b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_019c9670-f3e3-7300-8bf5-fb4cdd3f0b0d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesCurrent_019c9670-f3e3-7cd9-928a-4a14cc646c64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:to="loc_us-gaap_DerivativeLiabilitiesCurrent_019c9670-f3e3-7cd9-928a-4a14cc646c64" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesNoncurrent_019c9670-f3e3-7e2e-8371-3fe955168f63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_OtherFinancialDataLineItems_019c9670-f3e3-7e0f-969d-1eee1df37d3b" xlink:to="loc_us-gaap_DerivativeLiabilitiesNoncurrent_019c9670-f3e3-7e2e-8371-3fe955168f63" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/GoodwillandIntangibleassetsnetScheduleofIntangibleAssetsbyAssetClassDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#GoodwillandIntangibleassetsnetScheduleofIntangibleAssetsbyAssetClassDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/GoodwillandIntangibleassetsnetScheduleofIntangibleAssetsbyAssetClassDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-73ed-bfd9-74c5cd690d89" xlink:href="alit-20260331.xsd#alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillTable_019c9670-f3e3-7156-893a-d604e9909e91" xlink:href="alit-20260331.xsd#alit_ScheduleOfIntangibleAssetsOtherThanGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-73ed-bfd9-74c5cd690d89" xlink:to="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillTable_019c9670-f3e3-7156-893a-d604e9909e91" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-756c-97a0-4aadfd25d5d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillTable_019c9670-f3e3-7156-893a-d604e9909e91" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-756c-97a0-4aadfd25d5d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-756c-97a0-4aadfd25d5d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-756c-97a0-4aadfd25d5d9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-756c-97a0-4aadfd25d5d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-77c3-87c9-aa15a6d628fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-756c-97a0-4aadfd25d5d9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-77c3-87c9-aa15a6d628fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CustomerRelatedAndContractBasedIntangiblesMember_019c9670-f3e3-7cc8-af5b-9ed999079a90" xlink:href="alit-20260331.xsd#alit_CustomerRelatedAndContractBasedIntangiblesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-77c3-87c9-aa15a6d628fe" xlink:to="loc_alit_CustomerRelatedAndContractBasedIntangiblesMember_019c9670-f3e3-7cc8-af5b-9ed999079a90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_019c9670-f3e3-7001-85f0-793234d38173" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-77c3-87c9-aa15a6d628fe" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_019c9670-f3e3-7001-85f0-793234d38173" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019c9670-f3e3-7803-aea2-75725357ba7b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-77c3-87c9-aa15a6d628fe" xlink:to="loc_us-gaap_TradeNamesMember_019c9670-f3e3-7803-aea2-75725357ba7b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019c9670-f3e3-794f-8450-bde4bd230148" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-73ed-bfd9-74c5cd690d89" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019c9670-f3e3-794f-8450-bde4bd230148" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019c9670-f3e3-7153-9859-2bf48dd17e3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-73ed-bfd9-74c5cd690d89" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019c9670-f3e3-7153-9859-2bf48dd17e3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019c9670-f3e3-7d9c-996f-bb856c539122" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-73ed-bfd9-74c5cd690d89" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019c9670-f3e3-7d9c-996f-bb856c539122" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019c9670-f3e3-7865-b8ea-95de1ade2014" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-73ed-bfd9-74c5cd690d89" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019c9670-f3e3-7865-b8ea-95de1ade2014" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019c9670-f3e3-7bfe-8085-e58cb5f29007" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-73ed-bfd9-74c5cd690d89" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019c9670-f3e3-7bfe-8085-e58cb5f29007" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/GoodwillandIntangibleassetsnetScheduleofIntangibleAssetNetCarryingAmountandWeightedAverageRemainingUsefulLivesDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#GoodwillandIntangibleassetsnetScheduleofIntangibleAssetNetCarryingAmountandWeightedAverageRemainingUsefulLivesDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/GoodwillandIntangibleassetsnetScheduleofIntangibleAssetNetCarryingAmountandWeightedAverageRemainingUsefulLivesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-74e5-9e1b-34d64df10752" xlink:href="alit-20260331.xsd#alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillTable_019c9670-f3e3-77c6-833c-182bc8c889d4" xlink:href="alit-20260331.xsd#alit_ScheduleOfIntangibleAssetsOtherThanGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-74e5-9e1b-34d64df10752" xlink:to="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillTable_019c9670-f3e3-77c6-833c-182bc8c889d4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-74c1-9c40-4fab00a3d0f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillTable_019c9670-f3e3-77c6-833c-182bc8c889d4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-74c1-9c40-4fab00a3d0f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-74c1-9c40-4fab00a3d0f0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-74c1-9c40-4fab00a3d0f0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-74c1-9c40-4fab00a3d0f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-726c-a500-e293943a6096" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-74c1-9c40-4fab00a3d0f0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-726c-a500-e293943a6096" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CustomerRelatedAndContractBasedIntangiblesMember_019c9670-f3e3-73b1-b605-0900eeb120f0" xlink:href="alit-20260331.xsd#alit_CustomerRelatedAndContractBasedIntangiblesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-726c-a500-e293943a6096" xlink:to="loc_alit_CustomerRelatedAndContractBasedIntangiblesMember_019c9670-f3e3-73b1-b605-0900eeb120f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_019c9670-f3e3-706d-a2f1-56a5df94eafa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-726c-a500-e293943a6096" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_019c9670-f3e3-706d-a2f1-56a5df94eafa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019c9670-f3e3-76ed-849d-9503ed383506" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-726c-a500-e293943a6096" xlink:to="loc_us-gaap_TradeNamesMember_019c9670-f3e3-76ed-849d-9503ed383506" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019c9670-f3e3-7c93-88cb-6d3e114e79cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-74e5-9e1b-34d64df10752" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019c9670-f3e3-7c93-88cb-6d3e114e79cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019c9670-f3e3-7f45-accb-9057dbe4c895" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-74e5-9e1b-34d64df10752" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019c9670-f3e3-7f45-accb-9057dbe4c895" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019c9670-f3e3-711a-87a8-b1af53de7b8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_ScheduleOfIntangibleAssetsOtherThanGoodwillLineItems_019c9670-f3e3-74e5-9e1b-34d64df10752" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019c9670-f3e3-711a-87a8-b1af53de7b8e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/GoodwillandIntangibleassetsnetScheduleofIntangibleAssetsExpectedAnnualAmortizationExpenseDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#GoodwillandIntangibleassetsnetScheduleofIntangibleAssetsExpectedAnnualAmortizationExpenseDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/GoodwillandIntangibleassetsnetScheduleofIntangibleAssetsExpectedAnnualAmortizationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019c9670-f3e3-7d5e-bf26-5b97c411048d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019c9670-f3e3-7d5e-bf26-5b97c411048d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-7f41-afdb-47694394a914" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_019c9670-f3e3-7d5e-bf26-5b97c411048d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-7f41-afdb-47694394a914" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-7f41-afdb-47694394a914_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-7f41-afdb-47694394a914" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-7f41-afdb-47694394a914_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-7d38-ba98-cd54989f0a08" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019c9670-f3e3-7f41-afdb-47694394a914" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-7d38-ba98-cd54989f0a08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CustomerRelatedAndContractBasedIntangiblesMember_019c9670-f3e3-7011-b898-b9617de54384" xlink:href="alit-20260331.xsd#alit_CustomerRelatedAndContractBasedIntangiblesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-7d38-ba98-cd54989f0a08" xlink:to="loc_alit_CustomerRelatedAndContractBasedIntangiblesMember_019c9670-f3e3-7011-b898-b9617de54384" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_019c9670-f3e3-7ba8-9ded-0100522fb969" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-7d38-ba98-cd54989f0a08" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_019c9670-f3e3-7ba8-9ded-0100522fb969" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019c9670-f3e3-7526-bafc-4e2354a1115a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019c9670-f3e3-7d38-ba98-cd54989f0a08" xlink:to="loc_us-gaap_TradeNamesMember_019c9670-f3e3-7526-bafc-4e2354a1115a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019d4ed8-3133-7569-896c-73114b730387" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019d4ed8-3133-7569-896c-73114b730387" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019c9670-f3e3-7fee-abf3-8ae0c09d96a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019c9670-f3e3-7fee-abf3-8ae0c09d96a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019c9670-f3e3-7062-b573-8bb6b68e480b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019c9670-f3e3-7062-b573-8bb6b68e480b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019c9670-f3e3-7170-b80c-a9775d3eb88d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019c9670-f3e3-7170-b80c-a9775d3eb88d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019c9670-f3e3-700a-87dd-d427c892032a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019c9670-f3e3-700a-87dd-d427c892032a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour_019d4ed8-bd5b-78aa-823b-55d8e449abc0" xlink:href="alit-20260331.xsd#alit_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:to="loc_alit_FiniteLivedIntangibleAssetExpectedAmortizationAfterYearFour_019d4ed8-bd5b-78aa-823b-55d8e449abc0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019c9670-f3e3-7744-b434-cd7b08bbc683" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019c9670-f3e3-758d-80fb-b52a58385c7f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019c9670-f3e3-7744-b434-cd7b08bbc683" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/IncomeTaxesAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#IncomeTaxesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/IncomeTaxesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationLineItems_019d0704-82b6-7cee-b1c0-a28ae33d7295" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExaminationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationTable_019d0704-82b6-7cd7-8092-98e18b0529cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExaminationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019d0704-82b6-7cee-b1c0-a28ae33d7295" xlink:to="loc_us-gaap_IncomeTaxExaminationTable_019d0704-82b6-7cd7-8092-98e18b0529cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d0704-82b6-72d7-a943-37956d2a8459" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxExaminationTable_019d0704-82b6-7cd7-8092-98e18b0529cd" xlink:to="loc_srt_RangeAxis_019d0704-82b6-72d7-a943-37956d2a8459" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d0704-82b6-72d7-a943-37956d2a8459_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019d0704-82b6-72d7-a943-37956d2a8459" xlink:to="loc_srt_RangeMember_019d0704-82b6-72d7-a943-37956d2a8459_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d0704-82b6-7230-8f82-b0d9b784e546" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019d0704-82b6-72d7-a943-37956d2a8459" xlink:to="loc_srt_RangeMember_019d0704-82b6-7230-8f82-b0d9b784e546" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019d0704-82b6-75a8-8aa2-6e8a6a855f51" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d0704-82b6-7230-8f82-b0d9b784e546" xlink:to="loc_srt_MaximumMember_019d0704-82b6-75a8-8aa2-6e8a6a855f51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019d0704-82b6-7749-93a8-60d48f00ddb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019d0704-82b6-7cee-b1c0-a28ae33d7295" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_019d0704-82b6-7749-93a8-60d48f00ddb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019d0704-82b6-7180-88e7-33b337a3142c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExaminationLineItems_019d0704-82b6-7cee-b1c0-a28ae33d7295" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_019d0704-82b6-7180-88e7-33b337a3142c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/DebtScheduleofDebtOutstandingDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#DebtScheduleofDebtOutstandingDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/DebtScheduleofDebtOutstandingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-7ab4-9711-f3417bbe282f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-70bc-99ed-76307b2d4999" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-7ab4-9711-f3417bbe282f" xlink:to="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-70bc-99ed-76307b2d4999" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e3-7ff7-a718-b3becf594eb2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-70bc-99ed-76307b2d4999" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e3-7ff7-a718-b3becf594eb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-7ff7-a718-b3becf594eb2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e3-7ff7-a718-b3becf594eb2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-7ff7-a718-b3becf594eb2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-71e4-beac-b47d22260147" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e3-7ff7-a718-b3becf594eb2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-71e4-beac-b47d22260147" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SeventhIncrementalTermLoansMember_019c9670-f3e3-793c-a162-a1ca3504679b" xlink:href="alit-20260331.xsd#alit_SeventhIncrementalTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-71e4-beac-b47d22260147" xlink:to="loc_alit_SeventhIncrementalTermLoansMember_019c9670-f3e3-793c-a162-a1ca3504679b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019c9670-f3e3-7738-9ef6-788765a5f633" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-70bc-99ed-76307b2d4999" xlink:to="loc_us-gaap_CreditFacilityAxis_019c9670-f3e3-7738-9ef6-788765a5f633" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7738-9ef6-788765a5f633_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019c9670-f3e3-7738-9ef6-788765a5f633" xlink:to="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7738-9ef6-788765a5f633_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7b92-9d12-920b78245cd1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019c9670-f3e3-7738-9ef6-788765a5f633" xlink:to="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7b92-9d12-920b78245cd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AmendedRevolvingCreditFacilityMember_019c9670-f3e3-7b0a-baa6-23ca70c6b217" xlink:href="alit-20260331.xsd#alit_AmendedRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7b92-9d12-920b78245cd1" xlink:to="loc_alit_AmendedRevolvingCreditFacilityMember_019c9670-f3e3-7b0a-baa6-23ca70c6b217" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019c9670-f3e3-7a1f-8100-51d727612093" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-7ab4-9711-f3417bbe282f" xlink:to="loc_us-gaap_LongTermDebt_019c9670-f3e3-7a1f-8100-51d727612093" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019c9670-f3e3-7fab-9733-4e03b7cd602f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-7ab4-9711-f3417bbe282f" xlink:to="loc_us-gaap_LongTermDebtCurrent_019c9670-f3e3-7fab-9733-4e03b7cd602f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019c9670-f3e3-7711-b7ec-3ad8de507e35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-7ab4-9711-f3417bbe282f" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019c9670-f3e3-7711-b7ec-3ad8de507e35" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/DebtScheduleofDebtOutstandingFootnoteDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#DebtScheduleofDebtOutstandingFootnoteDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/DebtScheduleofDebtOutstandingFootnoteDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-79b8-a9d4-eaf5e30fa5f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-775f-b6ab-189184cae629" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-79b8-a9d4-eaf5e30fa5f1" xlink:to="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-775f-b6ab-189184cae629" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019c9670-f3e3-7dfb-a3a9-f257b4e347fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-775f-b6ab-189184cae629" xlink:to="loc_us-gaap_CreditFacilityAxis_019c9670-f3e3-7dfb-a3a9-f257b4e347fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7dfb-a3a9-f257b4e347fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019c9670-f3e3-7dfb-a3a9-f257b4e347fa" xlink:to="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7dfb-a3a9-f257b4e347fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7ac4-9bf9-54fd76375600" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019c9670-f3e3-7dfb-a3a9-f257b4e347fa" xlink:to="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7ac4-9bf9-54fd76375600" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AmendedRevolvingCreditFacilityMember_019c9670-f3e3-7178-9505-0ce854f1bc17" xlink:href="alit-20260331.xsd#alit_AmendedRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019c9670-f3e3-7ac4-9bf9-54fd76375600" xlink:to="loc_alit_AmendedRevolvingCreditFacilityMember_019c9670-f3e3-7178-9505-0ce854f1bc17" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e3-767e-8fba-2880468d9790" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-775f-b6ab-189184cae629" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e3-767e-8fba-2880468d9790" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-767e-8fba-2880468d9790_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e3-767e-8fba-2880468d9790" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-767e-8fba-2880468d9790_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-762a-b83b-04b58b63a586" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e3-767e-8fba-2880468d9790" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-762a-b83b-04b58b63a586" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SeventhIncrementalTermLoansMember_019c9670-f3e3-72fe-9e36-fe8519f176d1" xlink:href="alit-20260331.xsd#alit_SeventhIncrementalTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e3-762a-b83b-04b58b63a586" xlink:to="loc_alit_SeventhIncrementalTermLoansMember_019c9670-f3e3-72fe-9e36-fe8519f176d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019c9670-f3e3-7989-9da8-0e1332cb6968" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-79b8-a9d4-eaf5e30fa5f1" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019c9670-f3e3-7989-9da8-0e1332cb6968" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019c9670-f3e3-720c-9ed1-a5262ff92ad8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c9670-f3e3-79b8-a9d4-eaf5e30fa5f1" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019c9670-f3e3-720c-9ed1-a5262ff92ad8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/DebtAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#DebtAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/DebtAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-7953-bb27-be6d96c9fe13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-7953-bb27-be6d96c9fe13" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019d070a-1023-73e7-8950-b231c823399c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-7953-bb27-be6d96c9fe13" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019d070a-1023-73e7-8950-b231c823399c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019d070a-1023-73e7-8950-b231c823399c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019d070a-1023-73e7-8950-b231c823399c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019d070a-1023-73e7-8950-b231c823399c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019d070a-1023-729f-8ad0-ca259aa84254" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019d070a-1023-73e7-8950-b231c823399c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019d070a-1023-729f-8ad0-ca259aa84254" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SeventhIncrementalTermLoansMember_019d070a-1023-7b17-9c42-31b3879b6e14" xlink:href="alit-20260331.xsd#alit_SeventhIncrementalTermLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019d070a-1023-729f-8ad0-ca259aa84254" xlink:to="loc_alit_SeventhIncrementalTermLoansMember_019d070a-1023-7b17-9c42-31b3879b6e14" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AmendedTermLoanMember_019d070a-43fe-7d23-ae84-e61af2636b75" xlink:href="alit-20260331.xsd#alit_AmendedTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019d070a-1023-729f-8ad0-ca259aa84254" xlink:to="loc_alit_AmendedTermLoanMember_019d070a-43fe-7d23-ae84-e61af2636b75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019d070a-1023-70a4-a3a3-269dfbf575ae" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-7953-bb27-be6d96c9fe13" xlink:to="loc_srt_OwnershipAxis_019d070a-1023-70a4-a3a3-269dfbf575ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019d070a-1023-70a4-a3a3-269dfbf575ae_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019d070a-1023-70a4-a3a3-269dfbf575ae" xlink:to="loc_srt_OwnershipDomain_019d070a-1023-70a4-a3a3-269dfbf575ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019d070a-1023-7cc1-aa61-766347e796ab" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019d070a-1023-70a4-a3a3-269dfbf575ae" xlink:to="loc_srt_OwnershipDomain_019d070a-1023-7cc1-aa61-766347e796ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AlightHoldingsMember_019d070a-1023-701e-a0b9-2f59471d59c2" xlink:href="alit-20260331.xsd#alit_AlightHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019d070a-1023-7cc1-aa61-766347e796ab" xlink:to="loc_alit_AlightHoldingsMember_019d070a-1023-701e-a0b9-2f59471d59c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019d070a-43fe-78fe-b816-3d97678888ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c9670-f3e3-7953-bb27-be6d96c9fe13" xlink:to="loc_us-gaap_CreditFacilityAxis_019d070a-43fe-78fe-b816-3d97678888ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d070a-43fe-78fe-b816-3d97678888ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019d070a-43fe-78fe-b816-3d97678888ee" xlink:to="loc_us-gaap_CreditFacilityDomain_019d070a-43fe-78fe-b816-3d97678888ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019d070a-43fe-7059-8f1d-2dab8705de14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019d070a-43fe-78fe-b816-3d97678888ee" xlink:to="loc_us-gaap_CreditFacilityDomain_019d070a-43fe-7059-8f1d-2dab8705de14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AmendedRevolvingCreditFacilityMember_019d070a-43fe-7e80-a698-55b9e5f24e47" xlink:href="alit-20260331.xsd#alit_AmendedRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d070a-43fe-7059-8f1d-2dab8705de14" xlink:to="loc_alit_AmendedRevolvingCreditFacilityMember_019d070a-43fe-7e80-a698-55b9e5f24e47" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019d070a-43fe-7182-9ff1-a9d16eb5f22e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019d070a-43fe-7059-8f1d-2dab8705de14" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019d070a-43fe-7182-9ff1-a9d16eb5f22e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019d070a-1023-77e3-bf1d-fb30ecbdc29a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019d070a-1023-77e3-bf1d-fb30ecbdc29a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019d070a-1023-7f02-ac6a-f7fa3b6a3491" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019d070a-1023-7f02-ac6a-f7fa3b6a3491" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019d070a-43fe-77dc-9d5f-17136ef4376c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentPeriodicPaymentPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019d070a-43fe-77dc-9d5f-17136ef4376c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019d070a-43fe-7338-b7a0-1d40fbe85a32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019d070a-43fe-7338-b7a0-1d40fbe85a32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet_019d070a-43fe-7f9b-a499-2041164edc29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet_019d070a-43fe-7f9b-a499-2041164edc29" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_UnusedLettersOfCredit_019d070a-43fe-74cb-b8bd-eb5b7722d40e" xlink:href="alit-20260331.xsd#alit_UnusedLettersOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_alit_UnusedLettersOfCredit_019d070a-43fe-74cb-b8bd-eb5b7722d40e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_019d070a-43fe-7765-b4c0-59558c12737d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_019d070a-43fe-7765-b4c0-59558c12737d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityPeriodicPayment_019d070a-43ff-7fd2-964d-5333c97ad288" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityPeriodicPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_LineOfCreditFacilityPeriodicPayment_019d070a-43ff-7fd2-964d-5333c97ad288" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_019d070a-6104-7428-a588-6b9a0db66297" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d070a-1023-773b-947f-13f55d23e802" xlink:to="loc_us-gaap_InterestExpenseDebt_019d070a-6104-7428-a588-6b9a0db66297" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/StockholdersEquityAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#StockholdersEquityAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/StockholdersEquityAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-79ee-89e6-43f51fc13a64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-79ee-89e6-43f51fc13a64" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019db17f-bea9-795f-be90-cb4bc172b987" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-79ee-89e6-43f51fc13a64" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019db17f-bea9-795f-be90-cb4bc172b987" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-795f-be90-cb4bc172b987_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019db17f-bea9-795f-be90-cb4bc172b987" xlink:to="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-795f-be90-cb4bc172b987_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019db17f-bea9-795f-be90-cb4bc172b987" xlink:to="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019db17f-bea9-7a2f-bb00-3aae12083ae7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_us-gaap_CommonClassAMember_019db17f-bea9-7a2f-bb00-3aae12083ae7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_019db17f-ee74-799a-99c5-74b95b62282a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_us-gaap_CommonClassBMember_019db17f-ee74-799a-99c5-74b95b62282a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassBOneMember_019db17f-ee74-76c8-aa4a-1b84d7e4284e" xlink:href="alit-20260331.xsd#alit_CommonClassBOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_alit_CommonClassBOneMember_019db17f-ee74-76c8-aa4a-1b84d7e4284e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassBOneUnitsMember_019db180-1482-7cd6-9a66-6e0ab1e19dea" xlink:href="alit-20260331.xsd#alit_CommonClassBOneUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_alit_CommonClassBOneUnitsMember_019db180-1482-7cd6-9a66-6e0ab1e19dea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassBTwoMember_019db180-1482-7922-99f6-012d10c0b100" xlink:href="alit-20260331.xsd#alit_CommonClassBTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_alit_CommonClassBTwoMember_019db180-1482-7922-99f6-012d10c0b100" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassBTwoUnitsMember_019db180-389b-73ce-a739-9d6240c6d220" xlink:href="alit-20260331.xsd#alit_CommonClassBTwoUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_alit_CommonClassBTwoUnitsMember_019db180-389b-73ce-a739-9d6240c6d220" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassBThreeMember_019db180-389b-781f-af5f-fef4d1daca2b" xlink:href="alit-20260331.xsd#alit_CommonClassBThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_alit_CommonClassBThreeMember_019db180-389b-781f-af5f-fef4d1daca2b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassVMember_019db180-389b-7917-b684-2c9666b5a3d8" xlink:href="alit-20260331.xsd#alit_CommonClassVMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_alit_CommonClassVMember_019db180-389b-7917-b684-2c9666b5a3d8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassZUnitsMember_019db180-389b-7b19-a35f-5be68464f54a" xlink:href="alit-20260331.xsd#alit_CommonClassZUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_alit_CommonClassZUnitsMember_019db180-389b-7b19-a35f-5be68464f54a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ClassAUnitsMember_019db180-5b3b-717f-9bb1-22f3cccc8bc3" xlink:href="alit-20260331.xsd#alit_ClassAUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db17f-bea9-7544-b573-f2b4e465b42c" xlink:to="loc_alit_ClassAUnitsMember_019db180-5b3b-717f-9bb1-22f3cccc8bc3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019db180-1482-7141-98bd-70f7d2b7e9e6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-79ee-89e6-43f51fc13a64" xlink:to="loc_srt_OwnershipAxis_019db180-1482-7141-98bd-70f7d2b7e9e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019db180-1482-7141-98bd-70f7d2b7e9e6_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019db180-1482-7141-98bd-70f7d2b7e9e6" xlink:to="loc_srt_OwnershipDomain_019db180-1482-7141-98bd-70f7d2b7e9e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019db180-1482-7433-8109-78688b7468b6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019db180-1482-7141-98bd-70f7d2b7e9e6" xlink:to="loc_srt_OwnershipDomain_019db180-1482-7433-8109-78688b7468b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AlightHoldingsMember_019db180-1482-7492-9a2d-aef8c6ba77b6" xlink:href="alit-20260331.xsd#alit_AlightHoldingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019db180-1482-7433-8109-78688b7468b6" xlink:to="loc_alit_AlightHoldingsMember_019db180-1482-7492-9a2d-aef8c6ba77b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_019db17f-bea9-752c-9514-4769c30caac6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_019db17f-bea9-752c-9514-4769c30caac6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019db17f-bea9-7255-ac89-54dd2a1368b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019db17f-bea9-7255-ac89-54dd2a1368b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019db17f-bea9-77da-bf4c-1012f0b2e9fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019db17f-bea9-77da-bf4c-1012f0b2e9fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019db17f-bea9-759d-8bd0-d786bd70e21d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019db17f-bea9-759d-8bd0-d786bd70e21d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019db17f-bea9-7a04-96b7-ac70d5c3998d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019db17f-bea9-7a04-96b7-ac70d5c3998d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonStockNumberOfVotesPerShare_019db17f-bea9-7a68-bb1b-2c32d842447e" xlink:href="alit-20260331.xsd#alit_CommonStockNumberOfVotesPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_CommonStockNumberOfVotesPerShare_019db17f-bea9-7a68-bb1b-2c32d842447e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_IssuanceOfCommonUnits_019db17f-ee74-7ba6-b39e-caeab5493dfa" xlink:href="alit-20260331.xsd#alit_IssuanceOfCommonUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_IssuanceOfCommonUnits_019db17f-ee74-7ba6-b39e-caeab5493dfa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_NumberOfCommonStockInstruments_019db17f-ee74-7ed3-9583-b8c4e2104ee1" xlink:href="alit-20260331.xsd#alit_NumberOfCommonStockInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_NumberOfCommonStockInstruments_019db17f-ee74-7ed3-9583-b8c4e2104ee1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019db17f-ee74-734a-9a72-14eaf2f1dc8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_CommonStockSharesIssued_019db17f-ee74-734a-9a72-14eaf2f1dc8c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonStockConvertibleConversionRatio_019db17f-ee74-7ae4-b755-0ab3fb48eaa3" xlink:href="alit-20260331.xsd#alit_CommonStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_CommonStockConvertibleConversionRatio_019db17f-ee74-7ae4-b755-0ab3fb48eaa3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonStockSharesConvertibleStockPriceTrigger_019db17f-ee74-78e3-a891-a4189f0c7e43" xlink:href="alit-20260331.xsd#alit_CommonStockSharesConvertibleStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_CommonStockSharesConvertibleStockPriceTrigger_019db17f-ee74-78e3-a891-a4189f0c7e43" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonStockSharesConvertibleThresholdTradingDays_019db17f-ee74-7808-8799-bc17831a2c3b" xlink:href="alit-20260331.xsd#alit_CommonStockSharesConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_CommonStockSharesConvertibleThresholdTradingDays_019db17f-ee74-7808-8799-bc17831a2c3b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonStockSharesConvertibleThresholdConsecutiveTradingDays_019db17f-ee74-7154-9b20-d29543309f87" xlink:href="alit-20260331.xsd#alit_CommonStockSharesConvertibleThresholdConsecutiveTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_CommonStockSharesConvertibleThresholdConsecutiveTradingDays_019db17f-ee74-7154-9b20-d29543309f87" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonStockSharesConvertibleStockValuationPriceOnDilutedBasis_019db17f-ee74-74c7-b5c1-aaae687b8c47" xlink:href="alit-20260331.xsd#alit_CommonStockSharesConvertibleStockValuationPriceOnDilutedBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_CommonStockSharesConvertibleStockValuationPriceOnDilutedBasis_019db17f-ee74-74c7-b5c1-aaae687b8c47" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019db180-389b-7b86-a630-13a6b19355ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019db180-389b-7b86-a630-13a6b19355ac" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019db180-389b-7998-8dcf-9723ff4db651" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019db180-389b-7998-8dcf-9723ff4db651" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockSplits_019db180-389b-7223-9ac6-070fd87e7fda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockSplits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockSplits_019db180-389b-7223-9ac6-070fd87e7fda" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_StockholdersEquityHeldByNonControllingInterest_019db180-5b3b-7efc-b963-f7c4ae87351b" xlink:href="alit-20260331.xsd#alit_StockholdersEquityHeldByNonControllingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_StockholdersEquityHeldByNonControllingInterest_019db180-5b3b-7efc-b963-f7c4ae87351b" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonUnitsConversionRatio_019db180-5b3b-792d-8e74-d5b9caa02750" xlink:href="alit-20260331.xsd#alit_CommonUnitsConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_alit_CommonUnitsConversionRatio_019db180-5b3b-792d-8e74-d5b9caa02750" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019db180-7ad9-71a7-aab3-a993eb1df499" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019db180-7ad9-71a7-aab3-a993eb1df499" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019db180-7ad9-7837-a299-96894b7cc6d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019db17f-bea9-7e80-abb3-a3b95206565c" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019db180-7ad9-7837-a299-96894b7cc6d1" xlink:type="arc" order="20"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/StockholdersEquityScheduleofChangesinOutstandingStockDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#StockholdersEquityScheduleofChangesinOutstandingStockDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/StockholdersEquityScheduleofChangesinOutstandingStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-7c26-8800-9c12676c8787" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7f08-87d0-304f56b22fdd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-7c26-8800-9c12676c8787" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7f08-87d0-304f56b22fdd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e3-73ef-95ac-3998d573dccd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7f08-87d0-304f56b22fdd" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e3-73ef-95ac-3998d573dccd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-73ef-95ac-3998d573dccd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e3-73ef-95ac-3998d573dccd" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-73ef-95ac-3998d573dccd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7668-8b77-cc8200f992b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e3-73ef-95ac-3998d573dccd" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7668-8b77-cc8200f992b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassAUnitsMember_019c9670-f3e3-7a26-8ea5-81c70a7f78d0" xlink:href="alit-20260331.xsd#alit_CommonClassAUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7668-8b77-cc8200f992b9" xlink:to="loc_alit_CommonClassAUnitsMember_019c9670-f3e3-7a26-8ea5-81c70a7f78d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassB1Member_019c9670-f3e3-7582-8d6f-e26d6a78a2d4" xlink:href="alit-20260331.xsd#alit_CommonClassB1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7668-8b77-cc8200f992b9" xlink:to="loc_alit_CommonClassB1Member_019c9670-f3e3-7582-8d6f-e26d6a78a2d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassB2Member_019c9670-f3e3-78a8-9d1f-cb2d5bb79d69" xlink:href="alit-20260331.xsd#alit_CommonClassB2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7668-8b77-cc8200f992b9" xlink:to="loc_alit_CommonClassB2Member_019c9670-f3e3-78a8-9d1f-cb2d5bb79d69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassVMember_019c9670-f3e3-787f-95bb-5c45d43f0ba5" xlink:href="alit-20260331.xsd#alit_CommonClassVMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7668-8b77-cc8200f992b9" xlink:to="loc_alit_CommonClassVMember_019c9670-f3e3-787f-95bb-5c45d43f0ba5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassZMember_019c9670-f3e3-7ce8-b47c-e580a035bd9e" xlink:href="alit-20260331.xsd#alit_CommonClassZMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7668-8b77-cc8200f992b9" xlink:to="loc_alit_CommonClassZMember_019c9670-f3e3-7ce8-b47c-e580a035bd9e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e3-701d-9d86-aabc5c7e9099" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7f08-87d0-304f56b22fdd" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e3-701d-9d86-aabc5c7e9099" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-701d-9d86-aabc5c7e9099_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e3-701d-9d86-aabc5c7e9099" xlink:to="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-701d-9d86-aabc5c7e9099_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-799c-9ecb-9e03b9cd0ade" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e3-701d-9d86-aabc5c7e9099" xlink:to="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-799c-9ecb-9e03b9cd0ade" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019c9670-f3e3-79ae-9c91-2061a0fb7c5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-799c-9ecb-9e03b9cd0ade" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019c9670-f3e3-79ae-9c91-2061a0fb7c5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-7c26-8800-9c12676c8787" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019c9670-f3e3-753d-844b-892a54409564" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019c9670-f3e3-753d-844b-892a54409564" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019c9670-f3e3-7eba-b409-58ad8599ffc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019c9670-f3e3-7eba-b409-58ad8599ffc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_StockIssuedDuringPeriodSharesConversionOfNoncontrollingInterest_019c9670-f3e3-7d8e-8339-ba0ea8d80c0a" xlink:href="alit-20260331.xsd#alit_StockIssuedDuringPeriodSharesConversionOfNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:to="loc_alit_StockIssuedDuringPeriodSharesConversionOfNoncontrollingInterest_019c9670-f3e3-7d8e-8339-ba0ea8d80c0a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_019c9670-f3e3-7d95-aeb8-d04cbcb10c27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_019c9670-f3e3-7d95-aeb8-d04cbcb10c27" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019c9670-f3e3-7915-8e15-25e6abb4c2f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_019c9670-f3e3-7915-8e15-25e6abb4c2f8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_019c9670-f3e3-7119-9277-8fb2fc14f58e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_019c9670-f3e3-7119-9277-8fb2fc14f58e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019c9670-f3e3-75e9-b016-e49760593d90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019c9670-f3e3-75e9-b016-e49760593d90" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_019c9670-f3e3-7db2-81fe-512174c1ca92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c9670-f3e3-7a6c-b0b9-2087c1da47e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_019c9670-f3e3-7db2-81fe-512174c1ca92" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019c9670-f3e3-72d4-9a1e-5b873956ed25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019c9670-f3e3-742b-80ab-4f47e0f64a33" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/StockholdersEquityScheduleofChangesinAccumulatedOtherComprehensiveIncomeNetbyComponentDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#StockholdersEquityScheduleofChangesinAccumulatedOtherComprehensiveIncomeNetbyComponentDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/StockholdersEquityScheduleofChangesinAccumulatedOtherComprehensiveIncomeNetbyComponentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019c9670-f3e3-717e-8e6d-154a55bc9171" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019c9670-f3e3-7a6b-b5d4-85cb8739cd96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019c9670-f3e3-717e-8e6d-154a55bc9171" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019c9670-f3e3-7a6b-b5d4-85cb8739cd96" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e3-706a-aeb4-578f1845f0b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019c9670-f3e3-7a6b-b5d4-85cb8739cd96" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e3-706a-aeb4-578f1845f0b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-706a-aeb4-578f1845f0b5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e3-706a-aeb4-578f1845f0b5" xlink:to="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-706a-aeb4-578f1845f0b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-75f7-ba80-074a1c86ea74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e3-706a-aeb4-578f1845f0b5" xlink:to="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-75f7-ba80-074a1c86ea74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019c9670-f3e3-7a41-a1ac-692fa80609dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-75f7-ba80-074a1c86ea74" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019c9670-f3e3-7a41-a1ac-692fa80609dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019c9670-f3e3-7d23-85c0-f6dea17c8fd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-75f7-ba80-074a1c86ea74" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019c9670-f3e3-7d23-85c0-f6dea17c8fd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019c9670-f3e3-7aa5-9094-32415971c39f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c9670-f3e3-75f7-ba80-074a1c86ea74" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019c9670-f3e3-7aa5-9094-32415971c39f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019c9670-f3e3-717e-8e6d-154a55bc9171" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c9670-f3e3-7794-a7ea-44058ad6dc25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c9670-f3e3-7794-a7ea-44058ad6dc25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_019c9670-f3e3-77e6-bcf1-94d92c98d210" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_019c9670-f3e3-77e6-bcf1-94d92c98d210" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_019c9670-f3e3-7476-a557-9099e860548d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_019c9670-f3e3-7476-a557-9099e860548d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_019c9670-f3e3-784c-8e5a-1a707c4f7643" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_019c9670-f3e3-784c-8e5a-1a707c4f7643" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019c9670-f3e3-7df9-8909-172b02207928" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_019c9670-f3e3-7df9-8909-172b02207928" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodTax_019c9670-f3e3-743b-9a7f-752deb588a80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAociCurrentPeriodTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodTax_019c9670-f3e3-743b-9a7f-752deb588a80" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019c9670-f3e3-75ed-80db-0b8c256b46c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019c9670-f3e3-75ed-80db-0b8c256b46c1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019c9670-f3e3-7fea-aa7a-f9d9696fb39e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c9670-f3e3-7092-a6d5-d094b7273cfc" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019c9670-f3e3-7fea-aa7a-f9d9696fb39e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c9670-f3e3-7fab-b66e-9a82275d1012" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/ShareBasedCompensationAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#ShareBasedCompensationAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/ShareBasedCompensationAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7d76-8330-68572bc8998a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7d76-8330-68572bc8998a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019c9670-f3e3-7cba-a24d-c3cab7baef28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7d76-8330-68572bc8998a" xlink:to="loc_us-gaap_PlanNameAxis_019c9670-f3e3-7cba-a24d-c3cab7baef28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019c9670-f3e3-7cba-a24d-c3cab7baef28_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019c9670-f3e3-7cba-a24d-c3cab7baef28" xlink:to="loc_us-gaap_PlanNameDomain_019c9670-f3e3-7cba-a24d-c3cab7baef28_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019c9670-f3e3-72c3-9642-d8aa56afd612" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019c9670-f3e3-7cba-a24d-c3cab7baef28" xlink:to="loc_us-gaap_PlanNameDomain_019c9670-f3e3-72c3-9642-d8aa56afd612" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TwoThousandTwentyOneOmnibusIncentivePlanMember_019c9670-f3e3-7891-96ad-1f39ed799630" xlink:href="alit-20260331.xsd#alit_TwoThousandTwentyOneOmnibusIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019c9670-f3e3-72c3-9642-d8aa56afd612" xlink:to="loc_alit_TwoThousandTwentyOneOmnibusIncentivePlanMember_019c9670-f3e3-7891-96ad-1f39ed799630" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_EmployeeStockPurchasePlanMember_019c9670-f3e3-726e-b6e3-b8635dccdde9" xlink:href="alit-20260331.xsd#alit_EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019c9670-f3e3-72c3-9642-d8aa56afd612" xlink:to="loc_alit_EmployeeStockPurchasePlanMember_019c9670-f3e3-726e-b6e3-b8635dccdde9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c9670-f3e3-7edb-9233-32935662a9e3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7d76-8330-68572bc8998a" xlink:to="loc_srt_RangeAxis_019c9670-f3e3-7edb-9233-32935662a9e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c9670-f3e3-7edb-9233-32935662a9e3_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c9670-f3e3-7edb-9233-32935662a9e3" xlink:to="loc_srt_RangeMember_019c9670-f3e3-7edb-9233-32935662a9e3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c9670-f3e3-7eff-b78f-a633dce0f4b2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c9670-f3e3-7edb-9233-32935662a9e3" xlink:to="loc_srt_RangeMember_019c9670-f3e3-7eff-b78f-a633dce0f4b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019c9670-f3e3-70e9-9d5a-44944dae922c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c9670-f3e3-7eff-b78f-a633dce0f4b2" xlink:to="loc_srt_MinimumMember_019c9670-f3e3-70e9-9d5a-44944dae922c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c9670-f3e3-7432-89a7-4057d3a4a40f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c9670-f3e3-7eff-b78f-a633dce0f4b2" xlink:to="loc_srt_MaximumMember_019c9670-f3e3-7432-89a7-4057d3a4a40f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-7de8-9bd5-faa8fedf8a6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7d76-8330-68572bc8998a" xlink:to="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-7de8-9bd5-faa8fedf8a6d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7de8-9bd5-faa8fedf8a6d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-7de8-9bd5-faa8fedf8a6d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7de8-9bd5-faa8fedf8a6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7105-8112-a47cbcf3daa7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-7de8-9bd5-faa8fedf8a6d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7105-8112-a47cbcf3daa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TimeBasedRestrictedStockUnitsMember_019c9670-f3e3-71d0-ab45-0e7872e97136" xlink:href="alit-20260331.xsd#alit_TimeBasedRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7105-8112-a47cbcf3daa7" xlink:to="loc_alit_TimeBasedRestrictedStockUnitsMember_019c9670-f3e3-71d0-ab45-0e7872e97136" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e3-7a2a-b5fb-a9361ea5bed6" xlink:href="alit-20260331.xsd#alit_PerformanceBasedRestrictedStockUnitsPRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7105-8112-a47cbcf3daa7" xlink:to="loc_alit_PerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e3-7a2a-b5fb-a9361ea5bed6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_RestrictedStockUnitsRSUAndPerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e3-7bdd-ba47-ceafda96bf0a" xlink:href="alit-20260331.xsd#alit_RestrictedStockUnitsRSUAndPerformanceBasedRestrictedStockUnitsPRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7105-8112-a47cbcf3daa7" xlink:to="loc_alit_RestrictedStockUnitsRSUAndPerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e3-7bdd-ba47-ceafda96bf0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019c9670-f3e3-7221-93b8-71406c9188ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7105-8112-a47cbcf3daa7" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019c9670-f3e3-7221-93b8-71406c9188ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019c9670-f3e3-77ae-afee-a2d0c8130e7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7105-8112-a47cbcf3daa7" xlink:to="loc_us-gaap_EmployeeStockMember_019c9670-f3e3-77ae-afee-a2d0c8130e7d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e3-7860-b632-2071f3081edb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019c9670-f3e3-7d76-8330-68572bc8998a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e3-7860-b632-2071f3081edb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7860-b632-2071f3081edb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e3-7860-b632-2071f3081edb" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7860-b632-2071f3081edb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7710-addc-79f439d0579a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e3-7860-b632-2071f3081edb" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7710-addc-79f439d0579a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019c9670-f3e3-7788-be87-24443e22ad76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e3-7710-addc-79f439d0579a" xlink:to="loc_us-gaap_CommonClassAMember_019c9670-f3e3-7788-be87-24443e22ad76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019c9670-f3e3-7dea-b5d1-f47aa95059c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019c9670-f3e3-7dea-b5d1-f47aa95059c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PercentageOfUnitsGrantedSubjectToVestingRequirements_019c9670-f3e3-7ec9-8452-301085b349bb" xlink:href="alit-20260331.xsd#alit_PercentageOfUnitsGrantedSubjectToVestingRequirements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_alit_PercentageOfUnitsGrantedSubjectToVestingRequirements_019c9670-f3e3-7ec9-8452-301085b349bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019c9670-f3e3-7811-8c61-f57112ba8b67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019c9670-f3e3-7811-8c61-f57112ba8b67" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019c9670-f3e3-7a99-9cdd-8fcb91276207" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019c9670-f3e3-7a99-9cdd-8fcb91276207" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019c9670-f3e3-7ed8-ba4e-637dee9011a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_019c9670-f3e3-7ed8-ba4e-637dee9011a3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019c9670-f3e3-74a2-a2b1-99069bba6f4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019c9670-f3e3-74a2-a2b1-99069bba6f4b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ShareBasedCompensationArrangementByShareBasedPaymentAwardStockPlanPaymentPeriod_019c9670-f3e3-7795-a208-531302464c75" xlink:href="alit-20260331.xsd#alit_ShareBasedCompensationArrangementByShareBasedPaymentAwardStockPlanPaymentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_alit_ShareBasedCompensationArrangementByShareBasedPaymentAwardStockPlanPaymentPeriod_019c9670-f3e3-7795-a208-531302464c75" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfPayrollDeductionToPurchaseCommonStock_019c9670-f3e3-7aa6-bba4-9024f306a807" xlink:href="alit-20260331.xsd#alit_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfPayrollDeductionToPurchaseCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_alit_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfPayrollDeductionToPurchaseCommonStock_019c9670-f3e3-7aa6-bba4-9024f306a807" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee_019c9670-f3e3-7e87-8ca3-f377b6ecac72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee_019c9670-f3e3-7e87-8ca3-f377b6ecac72" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019c9670-f3e3-704b-9677-f0f071706a6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019c9670-f3e3-704b-9677-f0f071706a6d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019c9670-f3e3-76af-b108-bf82643c45a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019c9670-f3e3-76af-b108-bf82643c45a6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019c9670-f3e3-7903-be42-04926e004b1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_019c9670-f3e3-7903-be42-04926e004b1e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019c9670-f3e3-7833-96ce-7113d7cdefb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019c9670-f3e3-790d-8fa4-5575ea2d7a1d" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019c9670-f3e3-7833-96ce-7113d7cdefb7" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/ShareBasedCompensationSummaryofUnitActivityrelatedtoRSUsDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#ShareBasedCompensationSummaryofUnitActivityrelatedtoRSUsDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/ShareBasedCompensationSummaryofUnitActivityrelatedtoRSUsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c9670-f3e3-7a05-8102-18520768510c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c9670-f3e3-7d54-b65f-6798a2775e73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c9670-f3e3-7a05-8102-18520768510c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c9670-f3e3-7d54-b65f-6798a2775e73" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-7043-af99-ec7b80a31843" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c9670-f3e3-7d54-b65f-6798a2775e73" xlink:to="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-7043-af99-ec7b80a31843" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7043-af99-ec7b80a31843_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-7043-af99-ec7b80a31843" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7043-af99-ec7b80a31843_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7b8a-8d8d-1c66837e9567" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-7043-af99-ec7b80a31843" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7b8a-8d8d-1c66837e9567" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019c9670-f3e3-71b5-9ab7-dafdd3fc9d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7b8a-8d8d-1c66837e9567" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019c9670-f3e3-71b5-9ab7-dafdd3fc9d4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e3-72f1-a82c-e94ce7fe0765" xlink:href="alit-20260331.xsd#alit_PerformanceBasedRestrictedStockUnitsPRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7b8a-8d8d-1c66837e9567" xlink:to="loc_alit_PerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e3-72f1-a82c-e94ce7fe0765" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019c9670-f3e3-7fde-8bc7-dcb15b1e115a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c9670-f3e3-7a05-8102-18520768510c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019c9670-f3e3-7fde-8bc7-dcb15b1e115a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019c9670-f3e3-7895-8612-4097d0fc508c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019c9670-f3e3-7fde-8bc7-dcb15b1e115a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019c9670-f3e3-7895-8612-4097d0fc508c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019c9670-f3e3-7daf-90bd-753ca5fbba7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019c9670-f3e3-7fde-8bc7-dcb15b1e115a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019c9670-f3e3-7daf-90bd-753ca5fbba7f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019c9670-f3e3-706b-9b3a-f5b9b8577716" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019c9670-f3e3-7fde-8bc7-dcb15b1e115a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019c9670-f3e3-706b-9b3a-f5b9b8577716" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019c9670-f3e3-71ad-bda1-9ae0737fb6ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019c9670-f3e3-7fde-8bc7-dcb15b1e115a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019c9670-f3e3-71ad-bda1-9ae0737fb6ba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019c9670-f3e3-7ec2-8027-5eeffea6ecd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019c9670-f3e3-7801-889b-2ba27e7638ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c9670-f3e3-7a05-8102-18520768510c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019c9670-f3e3-7801-889b-2ba27e7638ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019c9670-f3e3-74f5-94fc-2a8cc167492b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019c9670-f3e3-7801-889b-2ba27e7638ef" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019c9670-f3e3-74f5-94fc-2a8cc167492b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019c9670-f3e3-747e-add6-555eb56314a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019c9670-f3e3-7801-889b-2ba27e7638ef" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019c9670-f3e3-747e-add6-555eb56314a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019c9670-f3e3-7212-9b3e-58fff3189913" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019c9670-f3e3-7801-889b-2ba27e7638ef" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019c9670-f3e3-7212-9b3e-58fff3189913" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019c9670-f3e3-7568-b583-ce4fe46a1227" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019c9670-f3e3-7801-889b-2ba27e7638ef" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019c9670-f3e3-7568-b583-ce4fe46a1227" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019c9670-f3e3-79b2-9a83-548f4ee460b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/ShareBasedCompensationScheduleofShareBasedCompensationCostsRelatedtoRSUsandPRSUsDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#ShareBasedCompensationScheduleofShareBasedCompensationCostsRelatedtoRSUsandPRSUsDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/ShareBasedCompensationScheduleofShareBasedCompensationCostsRelatedtoRSUsandPRSUsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c9670-f3e3-7a4c-869f-1f1b61be4a8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c9670-f3e3-76e5-8393-3b994972ce6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c9670-f3e3-7a4c-869f-1f1b61be4a8c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c9670-f3e3-76e5-8393-3b994972ce6a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-76eb-9720-966f76e1e6e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c9670-f3e3-76e5-8393-3b994972ce6a" xlink:to="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-76eb-9720-966f76e1e6e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-76eb-9720-966f76e1e6e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-76eb-9720-966f76e1e6e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-76eb-9720-966f76e1e6e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7af9-b959-4d6b96e1dd2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019c9670-f3e3-76eb-9720-966f76e1e6e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7af9-b959-4d6b96e1dd2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_RestrictedStockUnitsRSUAndPerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e3-7439-8e36-3288a82cebc8" xlink:href="alit-20260331.xsd#alit_RestrictedStockUnitsRSUAndPerformanceBasedRestrictedStockUnitsPRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c9670-f3e3-7af9-b959-4d6b96e1dd2e" xlink:to="loc_alit_RestrictedStockUnitsRSUAndPerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e3-7439-8e36-3288a82cebc8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019c9670-f3e3-770b-8a45-2c8aa82d87bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c9670-f3e3-76e5-8393-3b994972ce6a" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019c9670-f3e3-770b-8a45-2c8aa82d87bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019c9670-f3e3-770b-8a45-2c8aa82d87bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019c9670-f3e3-770b-8a45-2c8aa82d87bd" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019c9670-f3e3-770b-8a45-2c8aa82d87bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019c9670-f3e3-7b2e-9006-1247be044a22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019c9670-f3e3-770b-8a45-2c8aa82d87bd" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019c9670-f3e3-7b2e-9006-1247be044a22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_019c9670-f3e3-7215-a6c6-7980714cdcb1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c9670-f3e3-7b2e-9006-1247be044a22" xlink:to="loc_us-gaap_CostOfSalesMember_019c9670-f3e3-7215-a6c6-7980714cdcb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_019c9670-f3e3-7d3b-8119-aff81973cebc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c9670-f3e3-7b2e-9006-1247be044a22" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_019c9670-f3e3-7d3b-8119-aff81973cebc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019c9670-f3e3-7e0c-b549-6b88cfd491f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c9670-f3e3-7a4c-869f-1f1b61be4a8c" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019c9670-f3e3-7e0c-b549-6b88cfd491f2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/EarningsPerShareAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#EarningsPerShareAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/EarningsPerShareAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019c9670-f3e4-7828-a26e-292a9b010c43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019c9670-f3e4-72f0-bd2b-21b2e9f12ecb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019c9670-f3e4-7828-a26e-292a9b010c43" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019c9670-f3e4-72f0-bd2b-21b2e9f12ecb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e4-7041-9d76-95ca2c64b8ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019c9670-f3e4-72f0-bd2b-21b2e9f12ecb" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e4-7041-9d76-95ca2c64b8ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9670-f3e4-7041-9d76-95ca2c64b8ec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e4-7041-9d76-95ca2c64b8ec" xlink:to="loc_us-gaap_EquityComponentDomain_019c9670-f3e4-7041-9d76-95ca2c64b8ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9670-f3e4-7953-a7e7-229b77a3332f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9670-f3e4-7041-9d76-95ca2c64b8ec" xlink:to="loc_us-gaap_EquityComponentDomain_019c9670-f3e4-7953-a7e7-229b77a3332f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019c9670-f3e4-7678-87ed-6f0a6b50d0f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c9670-f3e4-7953-a7e7-229b77a3332f" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019c9670-f3e4-7678-87ed-6f0a6b50d0f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019c9670-f3e4-728d-a0c8-3a6d01b41884" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019c9670-f3e4-72f0-bd2b-21b2e9f12ecb" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019c9670-f3e4-728d-a0c8-3a6d01b41884" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019c9670-f3e4-728d-a0c8-3a6d01b41884_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019c9670-f3e4-728d-a0c8-3a6d01b41884" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019c9670-f3e4-728d-a0c8-3a6d01b41884_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019c9670-f3e4-711f-a19e-6b4b37ff9c43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019c9670-f3e4-728d-a0c8-3a6d01b41884" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019c9670-f3e4-711f-a19e-6b4b37ff9c43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019c9670-f3e4-761c-999c-6d53931549d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019c9670-f3e4-711f-a19e-6b4b37ff9c43" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019c9670-f3e4-761c-999c-6d53931549d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SellerEarnoutsMember_019c9670-f3e4-7c9a-8e7d-96ab853fc088" xlink:href="alit-20260331.xsd#alit_SellerEarnoutsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019c9670-f3e4-711f-a19e-6b4b37ff9c43" xlink:to="loc_alit_SellerEarnoutsMember_019c9670-f3e4-7c9a-8e7d-96ab853fc088" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e4-764c-a79e-2151ae8733c6" xlink:href="alit-20260331.xsd#alit_PerformanceBasedRestrictedStockUnitsPRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019c9670-f3e4-711f-a19e-6b4b37ff9c43" xlink:to="loc_alit_PerformanceBasedRestrictedStockUnitsPRSUsMember_019c9670-f3e4-764c-a79e-2151ae8733c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019c9670-f3e4-7d24-9f56-82baf48e8709" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019c9670-f3e4-7828-a26e-292a9b010c43" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019c9670-f3e4-7d24-9f56-82baf48e8709" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/SegmentReportingScheduleofCurrentReportableandRecastofSegmentsbyRevenueDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#SegmentReportingScheduleofCurrentReportableandRecastofSegmentsbyRevenueDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/SegmentReportingScheduleofCurrentReportableandRecastofSegmentsbyRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c9670-f3e4-7872-83d1-23336005e8b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c9670-f3e4-7872-83d1-23336005e8b8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019c9670-f3e4-75f8-ad35-05a99d178d19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c9670-f3e4-7872-83d1-23336005e8b8" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019c9670-f3e4-75f8-ad35-05a99d178d19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c9670-f3e4-75f8-ad35-05a99d178d19_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c9670-f3e4-75f8-ad35-05a99d178d19" xlink:to="loc_us-gaap_SegmentDomain_019c9670-f3e4-75f8-ad35-05a99d178d19_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c9670-f3e4-7fa9-9c9d-00830e82d565" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c9670-f3e4-75f8-ad35-05a99d178d19" xlink:to="loc_us-gaap_SegmentDomain_019c9670-f3e4-7fa9-9c9d-00830e82d565" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_EmployerSolutionsSegmentMember_019c9670-f3e4-7f1d-9414-3358815e6977" xlink:href="alit-20260331.xsd#alit_EmployerSolutionsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c9670-f3e4-7fa9-9c9d-00830e82d565" xlink:to="loc_alit_EmployerSolutionsSegmentMember_019c9670-f3e4-7f1d-9414-3358815e6977" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsAxis_019d0735-3cc8-753f-ae23-8abd9c08eac3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c9670-f3e4-7872-83d1-23336005e8b8" xlink:to="loc_us-gaap_SubsegmentsAxis_019d0735-3cc8-753f-ae23-8abd9c08eac3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019d0735-3cc8-753f-ae23-8abd9c08eac3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsegmentsAxis_019d0735-3cc8-753f-ae23-8abd9c08eac3" xlink:to="loc_us-gaap_SubsegmentsDomain_019d0735-3cc8-753f-ae23-8abd9c08eac3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsegmentsDomain_019d0735-3cc8-7697-b698-c247d279aef5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsegmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsegmentsAxis_019d0735-3cc8-753f-ae23-8abd9c08eac3" xlink:to="loc_us-gaap_SubsegmentsDomain_019d0735-3cc8-7697-b698-c247d279aef5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_RecurringMember_019d0735-3cc8-7f6d-ae17-1fdb958f8483" xlink:href="alit-20260331.xsd#alit_RecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019d0735-3cc8-7697-b698-c247d279aef5" xlink:to="loc_alit_RecurringMember_019d0735-3cc8-7f6d-ae17-1fdb958f8483" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ProjectsMember_019d0735-3cc8-7c7f-bb6e-2d7a6e3aec9e" xlink:href="alit-20260331.xsd#alit_ProjectsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsegmentsDomain_019d0735-3cc8-7697-b698-c247d279aef5" xlink:to="loc_alit_ProjectsMember_019d0735-3cc8-7c7f-bb6e-2d7a6e3aec9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019c9670-f3e4-7433-8db7-213776e2bd37" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c9670-f3e4-7872-83d1-23336005e8b8" xlink:to="loc_srt_ProductOrServiceAxis_019c9670-f3e4-7433-8db7-213776e2bd37" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019c9670-f3e4-7433-8db7-213776e2bd37_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019c9670-f3e4-7433-8db7-213776e2bd37" xlink:to="loc_srt_ProductsAndServicesDomain_019c9670-f3e4-7433-8db7-213776e2bd37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019c9670-f3e4-7e1e-89ac-72fda98b1f73" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019c9670-f3e4-7433-8db7-213776e2bd37" xlink:to="loc_srt_ProductsAndServicesDomain_019c9670-f3e4-7e1e-89ac-72fda98b1f73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyServiceMember_019c9670-f3e4-76ea-b1c0-234d9dc6499e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TechnologyServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c9670-f3e4-7e1e-89ac-72fda98b1f73" xlink:to="loc_us-gaap_TechnologyServiceMember_019c9670-f3e4-76ea-b1c0-234d9dc6499e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DeliveryCustomerCareAndOtherMember_019c9670-f3e4-7474-a694-5e95f9504a3f" xlink:href="alit-20260331.xsd#alit_DeliveryCustomerCareAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c9670-f3e4-7e1e-89ac-72fda98b1f73" xlink:to="loc_alit_DeliveryCustomerCareAndOtherMember_019c9670-f3e4-7474-a694-5e95f9504a3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019c9670-f3e4-70d8-a36d-b75e6b3c7143" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_RevenuesAbstract_019c9670-f3e4-70d8-a36d-b75e6b3c7143" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019c9670-f3e4-7698-a515-78db8b1cd6cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019c9670-f3e4-70d8-a36d-b75e6b3c7143" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019c9670-f3e4-7698-a515-78db8b1cd6cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_019c9670-f3e4-7d2a-95ea-5a1e8698a868" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_019c9670-f3e4-7d2a-95ea-5a1e8698a868" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_019c9670-f3e4-7df0-94bf-6e0f8600c62c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019c9670-f3e4-7d2a-95ea-5a1e8698a868" xlink:to="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_019c9670-f3e4-7df0-94bf-6e0f8600c62c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostDirectLabor_019c9670-f3e4-79c0-b456-eadcb2e8c2cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostDirectLabor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019c9670-f3e4-7d2a-95ea-5a1e8698a868" xlink:to="loc_us-gaap_CostDirectLabor_019c9670-f3e4-79c0-b456-eadcb2e8c2cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CostOfGoodsAndServicesSoldDepreciationOfFixedAssetsAndAmortizationOfInternallyDevelopedSoftwareAssets_019c9670-f3e4-7b7f-89b8-e737977c468b" xlink:href="alit-20260331.xsd#alit_CostOfGoodsAndServicesSoldDepreciationOfFixedAssetsAndAmortizationOfInternallyDevelopedSoftwareAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019c9670-f3e4-7d2a-95ea-5a1e8698a868" xlink:to="loc_alit_CostOfGoodsAndServicesSoldDepreciationOfFixedAssetsAndAmortizationOfInternallyDevelopedSoftwareAssets_019c9670-f3e4-7b7f-89b8-e737977c468b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_019c9670-f3e4-7d14-9a6d-67217878ad14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019c9670-f3e4-7d2a-95ea-5a1e8698a868" xlink:to="loc_us-gaap_GrossProfit_019c9670-f3e4-7d14-9a6d-67217878ad14" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019d0731-82d3-7a56-a5bf-d3c1be0ff6b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019d0731-82d3-7a56-a5bf-d3c1be0ff6b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_019c9670-f3e4-7745-9a4e-e0d8d061770c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_RestructuringCharges_019c9670-f3e4-7745-9a4e-e0d8d061770c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019c9670-f3e4-7ed7-85f7-56adce1e7e57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019c9670-f3e4-7ed7-85f7-56adce1e7e57" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_019c9670-f3e4-756d-880a-8b5eddf5f43b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_DepreciationAndAmortization_019c9670-f3e4-756d-880a-8b5eddf5f43b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019c9670-f3e4-78fd-8510-5ea89afcc1e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019c9670-f3e4-78fd-8510-5ea89afcc1e7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019c9670-f3e4-74dc-a094-e8ce7afe9953" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019c9670-f3e4-74dc-a094-e8ce7afe9953" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_019c9670-f3e4-75c1-9822-0a74d2780cb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c9670-f3e4-7374-8a02-114bf85804c9" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_019c9670-f3e4-75c1-9822-0a74d2780cb8" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/DerivativeFinancialInstrumentsScheduleofSwapAgreementsThatWillFixtheFloatingInterestRatesAssociatedWithItsTermLoanDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#DerivativeFinancialInstrumentsScheduleofSwapAgreementsThatWillFixtheFloatingInterestRatesAssociatedWithItsTermLoanDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/DerivativeFinancialInstrumentsScheduleofSwapAgreementsThatWillFixtheFloatingInterestRatesAssociatedWithItsTermLoanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7f0a-8231-6e23aa26a04a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativesFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019c9670-f3e4-72b1-a71b-0ad19d73f1e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7f0a-8231-6e23aa26a04a" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019c9670-f3e4-72b1-a71b-0ad19d73f1e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e4-7e8c-a152-2c6d97e5c875" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019c9670-f3e4-72b1-a71b-0ad19d73f1e5" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e4-7e8c-a152-2c6d97e5c875" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e4-7e8c-a152-2c6d97e5c875_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e4-7e8c-a152-2c6d97e5c875" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e4-7e8c-a152-2c6d97e5c875_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e4-7863-ac55-496adecd50e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019c9670-f3e4-7e8c-a152-2c6d97e5c875" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e4-7863-ac55-496adecd50e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_MarchTwoThousandAndTwentyTwoTermLoanMember_019c9670-f3e4-7a4d-ae05-383a3c104c22" xlink:href="alit-20260331.xsd#alit_MarchTwoThousandAndTwentyTwoTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e4-7863-ac55-496adecd50e0" xlink:to="loc_alit_MarchTwoThousandAndTwentyTwoTermLoanMember_019c9670-f3e4-7a4d-ae05-383a3c104c22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_MarchTwoThousandAndTwentyThreeTermLoanOneMember_019c9670-f3e4-7969-9b13-9c605686750c" xlink:href="alit-20260331.xsd#alit_MarchTwoThousandAndTwentyThreeTermLoanOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e4-7863-ac55-496adecd50e0" xlink:to="loc_alit_MarchTwoThousandAndTwentyThreeTermLoanOneMember_019c9670-f3e4-7969-9b13-9c605686750c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_MarchTwoThousandAndTwentyThreeTermLoanTwoMember_019c9670-f3e4-7e09-b1e6-9f7adcf9678c" xlink:href="alit-20260331.xsd#alit_MarchTwoThousandAndTwentyThreeTermLoanTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019c9670-f3e4-7863-ac55-496adecd50e0" xlink:to="loc_alit_MarchTwoThousandAndTwentyThreeTermLoanTwoMember_019c9670-f3e4-7e09-b1e6-9f7adcf9678c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c9670-f3e4-7ee1-ab80-54eb778f66ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019c9670-f3e4-72b1-a71b-0ad19d73f1e5" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c9670-f3e4-7ee1-ab80-54eb778f66ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e4-7ee1-ab80-54eb778f66ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c9670-f3e4-7ee1-ab80-54eb778f66ee" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e4-7ee1-ab80-54eb778f66ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e4-7bfb-94c2-cf12c3e0fe32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c9670-f3e4-7ee1-ab80-54eb778f66ee" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e4-7bfb-94c2-cf12c3e0fe32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019c9670-f3e4-7f5d-b984-4899d734e80f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c9670-f3e4-7bfb-94c2-cf12c3e0fe32" xlink:to="loc_us-gaap_InterestRateSwapMember_019c9670-f3e4-7f5d-b984-4899d734e80f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DerivativeInstrumentInitialNotionalAmount_019c9670-f3e4-7e28-8696-8eadf8bf268e" xlink:href="alit-20260331.xsd#alit_DerivativeInstrumentInitialNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7f0a-8231-6e23aa26a04a" xlink:to="loc_alit_DerivativeInstrumentInitialNotionalAmount_019c9670-f3e4-7e28-8696-8eadf8bf268e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019c9670-f3e4-73ea-8071-a71d9364f728" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7f0a-8231-6e23aa26a04a" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019c9670-f3e4-73ea-8071-a71d9364f728" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_019c9670-f3e4-75a7-a18f-db2c2e172ccd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7f0a-8231-6e23aa26a04a" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_019c9670-f3e4-75a7-a18f-db2c2e172ccd" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/DerivativeFinancialInstrumentsScheduleofFairValuesandLocationofOutstandingDerivativeInstrumentsRecordedintheCondensedConsolidatedBalanceSheetsDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#DerivativeFinancialInstrumentsScheduleofFairValuesandLocationofOutstandingDerivativeInstrumentsRecordedintheCondensedConsolidatedBalanceSheetsDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/DerivativeFinancialInstrumentsScheduleofFairValuesandLocationofOutstandingDerivativeInstrumentsRecordedintheCondensedConsolidatedBalanceSheetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7ce7-8b8a-3ac6ba4c1195" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativesFairValueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019c9670-f3e4-7d28-9d2a-dab8f2d96e25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7ce7-8b8a-3ac6ba4c1195" xlink:to="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019c9670-f3e4-7d28-9d2a-dab8f2d96e25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019c9670-f3e4-7062-916e-a0ddbbef9b73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_019c9670-f3e4-7d28-9d2a-dab8f2d96e25" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019c9670-f3e4-7062-916e-a0ddbbef9b73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f3e4-7062-916e-a0ddbbef9b73_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019c9670-f3e4-7062-916e-a0ddbbef9b73" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f3e4-7062-916e-a0ddbbef9b73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f3e4-7c72-bb24-ce656884728f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019c9670-f3e4-7062-916e-a0ddbbef9b73" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f3e4-7c72-bb24-ce656884728f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentAssetsMember_019c9670-f3e4-7da7-9dc3-11358be4a707" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f3e4-7c72-bb24-ce656884728f" xlink:to="loc_us-gaap_OtherCurrentAssetsMember_019c9670-f3e4-7da7-9dc3-11358be4a707" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_019c9670-f3e4-7564-b630-d98d1c999ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f3e4-7c72-bb24-ce656884728f" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_019c9670-f3e4-7564-b630-d98d1c999ec8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentLiabilitiesMember_019c9670-f3e4-7c8f-b5d3-c107b6d55767" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f3e4-7c72-bb24-ce656884728f" xlink:to="loc_us-gaap_OtherCurrentLiabilitiesMember_019c9670-f3e4-7c8f-b5d3-c107b6d55767" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_019c9670-f3e4-7dd9-820b-7ba91581255a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f3e4-7c72-bb24-ce656884728f" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_019c9670-f3e4-7dd9-820b-7ba91581255a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019c9670-f3e4-772f-875a-4114cbe3c5e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7ce7-8b8a-3ac6ba4c1195" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019c9670-f3e4-772f-875a-4114cbe3c5e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019c9670-f3e4-7c91-89c6-8204411d9339" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativesFairValueLineItems_019c9670-f3e4-7ce7-8b8a-3ac6ba4c1195" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019c9670-f3e4-7c91-89c6-8204411d9339" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/FinancialInstrumentsAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#FinancialInstrumentsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/FinancialInstrumentsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-7f19-b341-cf48f5ac03e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-7f19-b341-cf48f5ac03e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7f19-b341-cf48f5ac03e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-7f19-b341-cf48f5ac03e0" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7f19-b341-cf48f5ac03e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7a7d-8d59-2fd88aa000e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-7f19-b341-cf48f5ac03e0" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7a7d-8d59-2fd88aa000e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SellerEarnoutsLiabilityMember_019c9670-f3e4-7799-975c-7d1049734826" xlink:href="alit-20260331.xsd#alit_SellerEarnoutsLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7a7d-8d59-2fd88aa000e9" xlink:to="loc_alit_SellerEarnoutsLiabilityMember_019c9670-f3e4-7799-975c-7d1049734826" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019c9670-f3e4-7a04-b21a-41373c33d961" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019c9670-f3e4-7a04-b21a-41373c33d961" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7a04-b21a-41373c33d961_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019c9670-f3e4-7a04-b21a-41373c33d961" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7a04-b21a-41373c33d961_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7807-b825-1bbf5ab6d5ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019c9670-f3e4-7a04-b21a-41373c33d961" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7807-b825-1bbf5ab6d5ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019c9670-f3e4-7915-a7e9-cc0cb0d0cabe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7807-b825-1bbf5ab6d5ec" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019c9670-f3e4-7915-a7e9-cc0cb0d0cabe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019c9670-f3e4-744f-b696-168da8c0c7d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7807-b825-1bbf5ab6d5ec" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_019c9670-f3e4-744f-b696-168da8c0c7d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputMaturityMember_019c9670-f3e4-7cea-891f-a33653fb479a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputMaturityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7807-b825-1bbf5ab6d5ec" xlink:to="loc_us-gaap_MeasurementInputMaturityMember_019c9670-f3e4-7cea-891f-a33653fb479a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e4-7606-ac49-d3e24bb0f2a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e4-7606-ac49-d3e24bb0f2a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f3e4-7606-ac49-d3e24bb0f2a9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e4-7606-ac49-d3e24bb0f2a9" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f3e4-7606-ac49-d3e24bb0f2a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c9670-f3e4-7445-9c03-f140b4928770" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c9670-f3e4-7606-ac49-d3e24bb0f2a9" xlink:to="loc_us-gaap_ClassOfStockDomain_019c9670-f3e4-7445-9c03-f140b4928770" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019c9670-f3e4-76e7-9392-dc1a3d64ddf0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e4-7445-9c03-f140b4928770" xlink:to="loc_us-gaap_CommonClassAMember_019c9670-f3e4-76e7-9392-dc1a3d64ddf0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassZAMember_019c9670-f3e4-7030-a5ab-afccc9ba228e" xlink:href="alit-20260331.xsd#alit_CommonClassZAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e4-7445-9c03-f140b4928770" xlink:to="loc_alit_CommonClassZAMember_019c9670-f3e4-7030-a5ab-afccc9ba228e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommonClassZMember_019c9670-f3e4-7d91-961a-de7929a9688d" xlink:href="alit-20260331.xsd#alit_CommonClassZMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c9670-f3e4-7445-9c03-f140b4928770" xlink:to="loc_alit_CommonClassZMember_019c9670-f3e4-7d91-961a-de7929a9688d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019c9670-f3e4-7986-ba05-bf9a0d0a7263" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019c9670-f3e4-7986-ba05-bf9a0d0a7263" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f3e4-7986-ba05-bf9a0d0a7263_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019c9670-f3e4-7986-ba05-bf9a0d0a7263" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f3e4-7986-ba05-bf9a0d0a7263_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f3e4-7471-b1ce-c53c0344135d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019c9670-f3e4-7986-ba05-bf9a0d0a7263" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f3e4-7471-b1ce-c53c0344135d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019c9670-f3e4-7399-a15d-fdd987cc12d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019c9670-f3e4-7471-b1ce-c53c0344135d" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_019c9670-f3e4-7399-a15d-fdd987cc12d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019c9670-f3e4-7d53-82c3-6399255079f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019c9670-f3e4-7d53-82c3-6399255079f3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f3e4-7d53-82c3-6399255079f3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019c9670-f3e4-7d53-82c3-6399255079f3" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f3e4-7d53-82c3-6399255079f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f3e4-7041-baac-378149bfc13e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019c9670-f3e4-7d53-82c3-6399255079f3" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f3e4-7041-baac-378149bfc13e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DivestedBusinessMember_019c9670-f3e4-7fa0-a829-ae8a00ab604c" xlink:href="alit-20260331.xsd#alit_DivestedBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019c9670-f3e4-7041-baac-378149bfc13e" xlink:to="loc_alit_DivestedBusinessMember_019c9670-f3e4-7fa0-a829-ae8a00ab604c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_019c9670-f3e4-7b48-b1f2-489a5f4fe480" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:to="loc_us-gaap_ValuationTechniqueAxis_019c9670-f3e4-7b48-b1f2-489a5f4fe480" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019c9670-f3e4-7b48-b1f2-489a5f4fe480_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019c9670-f3e4-7b48-b1f2-489a5f4fe480" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019c9670-f3e4-7b48-b1f2-489a5f4fe480_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019c9670-f3e4-71e1-9bbf-591c6dcc79c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019c9670-f3e4-7b48-b1f2-489a5f4fe480" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019c9670-f3e4-71e1-9bbf-591c6dcc79c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeApproachValuationTechniqueMember_019c9670-f3e4-7bbb-8ec0-23285954670f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeApproachValuationTechniqueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019c9670-f3e4-71e1-9bbf-591c6dcc79c1" xlink:to="loc_us-gaap_IncomeApproachValuationTechniqueMember_019c9670-f3e4-7bbb-8ec0-23285954670f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c9670-f3e4-7c91-a339-c59910d5aedc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019c9670-f3e4-7f26-bbc6-766bf2d0340b" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c9670-f3e4-7c91-a339-c59910d5aedc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f3e4-7c91-a339-c59910d5aedc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c9670-f3e4-7c91-a339-c59910d5aedc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f3e4-7c91-a339-c59910d5aedc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f3e4-79c1-a117-04f588849d4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c9670-f3e4-7c91-a339-c59910d5aedc" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f3e4-79c1-a117-04f588849d4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019c9670-f3e4-7fe7-abef-d82259bcdbda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f3e4-79c1-a117-04f588849d4b" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019c9670-f3e4-7fe7-abef-d82259bcdbda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SellerEarnoutsPeriodToReceiveEarnOutShares_019c9670-f3e4-78ed-92f2-0ecf366f3be7" xlink:href="alit-20260331.xsd#alit_SellerEarnoutsPeriodToReceiveEarnOutShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_SellerEarnoutsPeriodToReceiveEarnOutShares_019c9670-f3e4-78ed-92f2-0ecf366f3be7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_FinancialInstrumentsSubjectToMandatoryRedemptionSettlementTermsSellerEarnOutFairValueOfShares_019c9670-f3e4-70f2-9904-c826b931f101" xlink:href="alit-20260331.xsd#alit_FinancialInstrumentsSubjectToMandatoryRedemptionSettlementTermsSellerEarnOutFairValueOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_FinancialInstrumentsSubjectToMandatoryRedemptionSettlementTermsSellerEarnOutFairValueOfShares_019c9670-f3e4-70f2-9904-c826b931f101" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_LossGainFromChangeInFairValueOfSellerEarnouts_019c9670-f3e4-7e4c-92a6-ee14e6ee2247" xlink:href="alit-20260331.xsd#alit_LossGainFromChangeInFairValueOfSellerEarnouts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_LossGainFromChangeInFairValueOfSellerEarnouts_019c9670-f3e4-7e4c-92a6-ee14e6ee2247" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_019c9670-f3e4-775f-9007-0b3253238da6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_019c9670-f3e4-775f-9007-0b3253238da6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_BusinessCombinationContingentConsiderationLiabilityExpectedHoldingPeriod_019c9670-f3e4-7766-a525-4231d3b2eead" xlink:href="alit-20260331.xsd#alit_BusinessCombinationContingentConsiderationLiabilityExpectedHoldingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_BusinessCombinationContingentConsiderationLiabilityExpectedHoldingPeriod_019c9670-f3e4-7766-a525-4231d3b2eead" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019c9670-f3e4-7b88-b7c2-7d8da56b96d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_019c9670-f3e4-7b88-b7c2-7d8da56b96d7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssuedPricePerShare_019c9670-f3e4-770d-84e3-3e4c6d6ad17e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssuedPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_us-gaap_SharesIssuedPricePerShare_019c9670-f3e4-770d-84e3-3e4c6d6ad17e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_EquityInstrumentsContingentConsiderationLiabilityFairValueDisclosure_019c9670-f3e4-7a7c-aae0-80ad565987b6" xlink:href="alit-20260331.xsd#alit_EquityInstrumentsContingentConsiderationLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_EquityInstrumentsContingentConsiderationLiabilityFairValueDisclosure_019c9670-f3e4-7a7c-aae0-80ad565987b6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmount_019c9670-f3e4-70f9-965d-5db89464b16b" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmount_019c9670-f3e4-70f9-965d-5db89464b16b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmountFairValue_019c9670-f3e4-7092-8357-a8d1ea449464" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmountFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationContingentConsiderationAggregatePrincipalAmountFairValue_019c9670-f3e4-7092-8357-a8d1ea449464" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_OtherAssetsConsiderationReceivableSellerNoteFairValue_019c9670-f3e4-7294-9f19-e5dff728178d" xlink:href="alit-20260331.xsd#alit_OtherAssetsConsiderationReceivableSellerNoteFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_OtherAssetsConsiderationReceivableSellerNoteFairValue_019c9670-f3e4-7294-9f19-e5dff728178d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_GainLossFromChangeInFairValueOfFinancialInstruments_019c9670-f3e4-77b4-9ea7-3d54dd2a4160" xlink:href="alit-20260331.xsd#alit_GainLossFromChangeInFairValueOfFinancialInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_GainLossFromChangeInFairValueOfFinancialInstruments_019c9670-f3e4-77b4-9ea7-3d54dd2a4160" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AdditionalSellerNoteMeasurementBasis_019c9670-f3e4-7aae-9112-22dea94ff5fd" xlink:href="alit-20260331.xsd#alit_AdditionalSellerNoteMeasurementBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019c9670-f3e4-73f2-a460-5853ef496411" xlink:to="loc_alit_AdditionalSellerNoteMeasurementBasis_019c9670-f3e4-7aae-9112-22dea94ff5fd" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/TaxReceivableAgreementAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#TaxReceivableAgreementAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/TaxReceivableAgreementAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019c9670-f3e4-7228-bbec-2a3effcb7ca0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019c9670-f3e4-7dfd-9acb-0749d6ac730c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019c9670-f3e4-7228-bbec-2a3effcb7ca0" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019c9670-f3e4-7dfd-9acb-0749d6ac730c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-7fd5-a3bd-5a0ba590f26d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019c9670-f3e4-7dfd-9acb-0749d6ac730c" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-7fd5-a3bd-5a0ba590f26d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7fd5-a3bd-5a0ba590f26d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-7fd5-a3bd-5a0ba590f26d" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7fd5-a3bd-5a0ba590f26d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7fb2-bc18-e2a0558f77fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-7fd5-a3bd-5a0ba590f26d" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7fb2-bc18-e2a0558f77fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementLiabilityMember_019c9670-f3e4-7bfa-8721-c41a103d8c07" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7fb2-bc18-e2a0558f77fc" xlink:to="loc_alit_TaxReceivableAgreementLiabilityMember_019c9670-f3e4-7bfa-8721-c41a103d8c07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementLiabilityDiscountedMember_019c9670-f3e4-78e1-a4a6-d46c5e27bfa6" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementLiabilityDiscountedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7fb2-bc18-e2a0558f77fc" xlink:to="loc_alit_TaxReceivableAgreementLiabilityDiscountedMember_019c9670-f3e4-78e1-a4a6-d46c5e27bfa6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementLiabilityUndiscountedMember_019c9670-f3e4-73ba-858f-ce133b41b492" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementLiabilityUndiscountedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-7fb2-bc18-e2a0558f77fc" xlink:to="loc_alit_TaxReceivableAgreementLiabilityUndiscountedMember_019c9670-f3e4-73ba-858f-ce133b41b492" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019c9670-f3e4-7ec2-8571-412928193589" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_019c9670-f3e4-7dfd-9acb-0749d6ac730c" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019c9670-f3e4-7ec2-8571-412928193589" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7ec2-8571-412928193589_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019c9670-f3e4-7ec2-8571-412928193589" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7ec2-8571-412928193589_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7c41-be6c-8655f057ceb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019c9670-f3e4-7ec2-8571-412928193589" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7c41-be6c-8655f057ceb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019c9670-f3e4-7572-aa55-399516339cd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019c9670-f3e4-7c41-be6c-8655f057ceb8" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019c9670-f3e4-7572-aa55-399516339cd9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_EffectiveIncomeTaxRateReconciliationFederalStateAndLocalIncomeTaxRate_019c9670-f3e4-7938-98c5-2a5bf44a3cb3" xlink:href="alit-20260331.xsd#alit_EffectiveIncomeTaxRateReconciliationFederalStateAndLocalIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019c9670-f3e4-7228-bbec-2a3effcb7ca0" xlink:to="loc_alit_EffectiveIncomeTaxRateReconciliationFederalStateAndLocalIncomeTaxRate_019c9670-f3e4-7938-98c5-2a5bf44a3cb3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_019c9670-f3e4-7063-8464-1ffc4b351d42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019c9670-f3e4-7228-bbec-2a3effcb7ca0" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_019c9670-f3e4-7063-8464-1ffc4b351d42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityConversionOfNoncontrollingInterest_019c9670-f3e4-722e-989c-18f116e2b065" xlink:href="alit-20260331.xsd#alit_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityConversionOfNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019c9670-f3e4-7228-bbec-2a3effcb7ca0" xlink:to="loc_alit_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityConversionOfNoncontrollingInterest_019c9670-f3e4-722e-989c-18f116e2b065" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019c9670-f3e4-7e5b-b1e3-9c3f1f994854" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019c9670-f3e4-7228-bbec-2a3effcb7ca0" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019c9670-f3e4-7e5b-b1e3-9c3f1f994854" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementObligationsPaid_019db187-50f4-7aad-96d3-8f3e38a2b5a2" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementObligationsPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019c9670-f3e4-7228-bbec-2a3effcb7ca0" xlink:to="loc_alit_TaxReceivableAgreementObligationsPaid_019db187-50f4-7aad-96d3-8f3e38a2b5a2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementObligationsPotentialIncreaseToPayments_019c9670-f3e4-7057-9240-fb84f2830ef1" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementObligationsPotentialIncreaseToPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_019c9670-f3e4-7228-bbec-2a3effcb7ca0" xlink:to="loc_alit_TaxReceivableAgreementObligationsPotentialIncreaseToPayments_019c9670-f3e4-7057-9240-fb84f2830ef1" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/TaxReceivableAgreementSummaryofChangestoTRALiabilityDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#TaxReceivableAgreementSummaryofChangestoTRALiabilityDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/TaxReceivableAgreementSummaryofChangestoTRALiabilityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019c9670-f3e4-7f68-8945-acb083a9d3c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019c9670-f3e4-74a6-87c8-d70ff61fe9c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019c9670-f3e4-7f68-8945-acb083a9d3c0" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019c9670-f3e4-74a6-87c8-d70ff61fe9c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-799b-8e88-8c02d51136db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019c9670-f3e4-74a6-87c8-d70ff61fe9c0" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-799b-8e88-8c02d51136db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-799b-8e88-8c02d51136db_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-799b-8e88-8c02d51136db" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-799b-8e88-8c02d51136db_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-725c-b385-52072ad3afee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019c9670-f3e4-799b-8e88-8c02d51136db" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-725c-b385-52072ad3afee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementLiabilityMember_019c9670-f3e4-7f27-8b7d-737840d38858" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c9670-f3e4-725c-b385-52072ad3afee" xlink:to="loc_alit_TaxReceivableAgreementLiabilityMember_019c9670-f3e4-7f27-8b7d-737840d38858" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019c9670-f3e4-79e7-858c-078567e639a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019c9670-f3e4-7f68-8945-acb083a9d3c0" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019c9670-f3e4-79e7-858c-078567e639a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019c9670-f3e4-787e-a0f4-22a9b3ea1f89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019c9670-f3e4-79e7-858c-078567e639a6" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019c9670-f3e4-787e-a0f4-22a9b3ea1f89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityFairValuePremeasurement_019c9670-f3e4-7da8-a529-b643338a7438" xlink:href="alit-20260331.xsd#alit_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityFairValuePremeasurement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019c9670-f3e4-79e7-858c-078567e639a6" xlink:to="loc_alit_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityFairValuePremeasurement_019c9670-f3e4-7da8-a529-b643338a7438" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease_019c9670-f3e4-7ad5-a1c7-038d85c1d979" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019c9670-f3e4-79e7-858c-078567e639a6" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease_019c9670-f3e4-7ad5-a1c7-038d85c1d979" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019c9670-f3e4-7947-a1c7-5e5f9facb9c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementObligationsCurrent_019c9670-f3e4-7769-98ba-a5e8d16957ab" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementObligationsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019c9670-f3e4-7f68-8945-acb083a9d3c0" xlink:to="loc_alit_TaxReceivableAgreementObligationsCurrent_019c9670-f3e4-7769-98ba-a5e8d16957ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementObligationsNoncurrent_019c9670-f3e4-7b82-8814-044b54580ea2" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementObligationsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019c9670-f3e4-7f68-8945-acb083a9d3c0" xlink:to="loc_alit_TaxReceivableAgreementObligationsNoncurrent_019c9670-f3e4-7b82-8814-044b54580ea2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/FairValueMeasurementScheduleofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#FairValueMeasurementScheduleofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/FairValueMeasurementScheduleofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019c9670-f49f-7db0-836c-ea83663057d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019c9670-f3e4-722a-be90-96fd257104bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019c9670-f49f-7db0-836c-ea83663057d3" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019c9670-f3e4-722a-be90-96fd257104bb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c9670-f49f-7b5f-9eb6-c73cf7e4b573" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019c9670-f3e4-722a-be90-96fd257104bb" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c9670-f49f-7b5f-9eb6-c73cf7e4b573" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f49f-7b5f-9eb6-c73cf7e4b573_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c9670-f49f-7b5f-9eb6-c73cf7e4b573" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f49f-7b5f-9eb6-c73cf7e4b573_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f49f-71b7-bceb-d51f52e204b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c9670-f49f-7b5f-9eb6-c73cf7e4b573" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f49f-71b7-bceb-d51f52e204b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019c9670-f49f-7c88-9dd9-cdb4a4b954bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f49f-71b7-bceb-d51f52e204b3" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019c9670-f49f-7c88-9dd9-cdb4a4b954bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019c9670-f49f-734e-ad12-1ee093edc895" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f49f-71b7-bceb-d51f52e204b3" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019c9670-f49f-734e-ad12-1ee093edc895" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019c9670-f49f-7d04-982e-1f8300f8838a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c9670-f49f-71b7-bceb-d51f52e204b3" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019c9670-f49f-7d04-982e-1f8300f8838a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019c9670-f49f-7248-863a-43c3bd0ccbef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019c9670-f49f-7db0-836c-ea83663057d3" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019c9670-f49f-7248-863a-43c3bd0ccbef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019c9670-f49f-764a-88e3-6255cca01dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019c9670-f49f-7248-863a-43c3bd0ccbef" xlink:to="loc_us-gaap_DerivativeAssets_019c9670-f49f-764a-88e3-6255cca01dc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_AdditionalSellerNoteFairValueDisclosure_019c9670-f49f-7d06-9731-19715c63cadd" xlink:href="alit-20260331.xsd#alit_AdditionalSellerNoteFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019c9670-f49f-7248-863a-43c3bd0ccbef" xlink:to="loc_alit_AdditionalSellerNoteFairValueDisclosure_019c9670-f49f-7d06-9731-19715c63cadd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019c9670-f49f-72a4-92a9-670646206ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019c9670-f49f-7248-863a-43c3bd0ccbef" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019c9670-f49f-72a4-92a9-670646206ef2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019c9670-f49f-7025-b7c2-0e2f14e4cab7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019c9670-f49f-7db0-836c-ea83663057d3" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019c9670-f49f-7025-b7c2-0e2f14e4cab7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019c9670-f49f-7bab-951d-dee400411ba8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019c9670-f49f-7025-b7c2-0e2f14e4cab7" xlink:to="loc_us-gaap_DerivativeLiabilities_019c9670-f49f-7bab-951d-dee400411ba8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_SellerEarnoutsLiabilityFairValueDisclosure_019c9670-f49f-737e-9692-7c05b70945c6" xlink:href="alit-20260331.xsd#alit_SellerEarnoutsLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019c9670-f49f-7025-b7c2-0e2f14e4cab7" xlink:to="loc_alit_SellerEarnoutsLiabilityFairValueDisclosure_019c9670-f49f-737e-9692-7c05b70945c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TaxReceivableAgreementLiabilityFairValueDisclosure_019c9670-f49f-74ed-a5a8-ac15a815d8c9" xlink:href="alit-20260331.xsd#alit_TaxReceivableAgreementLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019c9670-f49f-7025-b7c2-0e2f14e4cab7" xlink:to="loc_alit_TaxReceivableAgreementLiabilityFairValueDisclosure_019c9670-f49f-74ed-a5a8-ac15a815d8c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019c9670-f49f-76cf-9f1b-fae7b3a831e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_019c9670-f49f-7025-b7c2-0e2f14e4cab7" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019c9670-f49f-76cf-9f1b-fae7b3a831e0" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/FairValueMeasurementScheduleofFairValueofDebtClassifiedasLevel2WithinFairvalueHierarchyDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#FairValueMeasurementScheduleofFairValueofDebtClassifiedasLevel2WithinFairvalueHierarchyDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/FairValueMeasurementScheduleofFairValueofDebtClassifiedasLevel2WithinFairvalueHierarchyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d0753-f000-74e1-85bb-4c3394599e20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d0753-f000-773f-8127-bfe00da173a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d0753-f000-74e1-85bb-4c3394599e20" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d0753-f000-773f-8127-bfe00da173a7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019d0753-f000-706e-ae2b-16ba7030d239" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019d0753-f000-773f-8127-bfe00da173a7" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019d0753-f000-706e-ae2b-16ba7030d239" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019d0753-f000-706e-ae2b-16ba7030d239_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019d0753-f000-706e-ae2b-16ba7030d239" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019d0753-f000-706e-ae2b-16ba7030d239_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019d0756-2e86-706e-bbf1-bbd622ac408a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019d0753-f000-706e-ae2b-16ba7030d239" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019d0756-2e86-706e-bbf1-bbd622ac408a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019d0753-f000-74b2-9c38-1f0de0604245" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019d0756-2e86-706e-bbf1-bbd622ac408a" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019d0753-f000-74b2-9c38-1f0de0604245" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019d0753-f000-7b49-8e4e-3a073a5821f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019d0753-f000-74b2-9c38-1f0de0604245" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019d0753-f000-7b49-8e4e-3a073a5821f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019d0753-f000-7487-a38c-eb856731b93b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019d0753-f000-74b2-9c38-1f0de0604245" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019d0753-f000-7487-a38c-eb856731b93b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmountFairValue_019d0753-f000-71db-9790-9b6fce49064b" xlink:href="alit-20260331.xsd#alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmountFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d0753-f000-74e1-85bb-4c3394599e20" xlink:to="loc_alit_DisposalGroupIncludingDiscontinuedOperationConsiderationAggregatePrincipalAmountFairValue_019d0753-f000-71db-9790-9b6fce49064b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019d0753-f000-7729-b74f-62b9144cd8f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d0753-f000-74e1-85bb-4c3394599e20" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019d0753-f000-7729-b74f-62b9144cd8f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_019d0753-f000-7177-8a8a-0f69e498dd8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d0753-f000-74e1-85bb-4c3394599e20" xlink:to="loc_us-gaap_LongTermDebtCurrent_019d0753-f000-7177-8a8a-0f69e498dd8d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_019d0753-f000-70fe-954f-c82736ece846" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d0753-f000-74e1-85bb-4c3394599e20" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_019d0753-f000-70fe-954f-c82736ece846" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019d0753-f000-740f-9e5d-32784418bb28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019d0753-f000-74e1-85bb-4c3394599e20" xlink:to="loc_us-gaap_LongTermDebt_019d0753-f000-740f-9e5d-32784418bb28" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/RestructuringAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#RestructuringAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/RestructuringAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-784e-96c6-0f2bada1a802" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-75fa-b30e-496c84ccdd60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-784e-96c6-0f2bada1a802" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-75fa-b30e-496c84ccdd60" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-741c-aca0-d38d3472a6e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-75fa-b30e-496c84ccdd60" xlink:to="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-741c-aca0-d38d3472a6e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-741c-aca0-d38d3472a6e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-741c-aca0-d38d3472a6e1" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-741c-aca0-d38d3472a6e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-79b4-834d-e51edc72f530" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-741c-aca0-d38d3472a6e1" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-79b4-834d-e51edc72f530" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TwoYearStrategicTransformationRestructuringProgramMember_019c9670-f49f-7c03-8fcb-77a9be3a88a4" xlink:href="alit-20260331.xsd#alit_TwoYearStrategicTransformationRestructuringProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-79b4-834d-e51edc72f530" xlink:to="loc_alit_TwoYearStrategicTransformationRestructuringProgramMember_019c9670-f49f-7c03-8fcb-77a9be3a88a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ManagementInitiatedRestructuringAndIntegrationPlanMember_019c9670-f49f-7396-b92e-c5a70f81e11f" xlink:href="alit-20260331.xsd#alit_ManagementInitiatedRestructuringAndIntegrationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-79b4-834d-e51edc72f530" xlink:to="loc_alit_ManagementInitiatedRestructuringAndIntegrationPlanMember_019c9670-f49f-7396-b92e-c5a70f81e11f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PostSeparationPlanMember_019c9670-f49f-7d76-9714-16f8a81f289c" xlink:href="alit-20260331.xsd#alit_PostSeparationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-79b4-834d-e51edc72f530" xlink:to="loc_alit_PostSeparationPlanMember_019c9670-f49f-7d76-9714-16f8a81f289c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7d40-b7cb-7c970d209534" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-75fa-b30e-496c84ccdd60" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7d40-b7cb-7c970d209534" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7d40-b7cb-7c970d209534_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7d40-b7cb-7c970d209534" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7d40-b7cb-7c970d209534_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-729e-9c93-e009aea4b353" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7d40-b7cb-7c970d209534" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-729e-9c93-e009aea4b353" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_019c9670-f49f-7a40-b10b-5e015f178242" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-729e-9c93-e009aea4b353" xlink:to="loc_us-gaap_EmployeeSeveranceMember_019c9670-f49f-7a40-b10b-5e015f178242" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_019c9670-f49f-785a-b89f-aa4261eb12e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-729e-9c93-e009aea4b353" xlink:to="loc_us-gaap_OtherRestructuringMember_019c9670-f49f-785a-b89f-aa4261eb12e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c9670-f49f-7686-ad4d-8b0fd68b288b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-75fa-b30e-496c84ccdd60" xlink:to="loc_srt_RangeAxis_019c9670-f49f-7686-ad4d-8b0fd68b288b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c9670-f49f-7686-ad4d-8b0fd68b288b_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c9670-f49f-7686-ad4d-8b0fd68b288b" xlink:to="loc_srt_RangeMember_019c9670-f49f-7686-ad4d-8b0fd68b288b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c9670-f49f-7559-a1e8-b1f1d40ac45d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c9670-f49f-7686-ad4d-8b0fd68b288b" xlink:to="loc_srt_RangeMember_019c9670-f49f-7559-a1e8-b1f1d40ac45d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019c9670-f49f-7b9e-a4ca-381e39101a90" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c9670-f49f-7559-a1e8-b1f1d40ac45d" xlink:to="loc_srt_MinimumMember_019c9670-f49f-7b9e-a4ca-381e39101a90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c9670-f49f-72b6-8082-fbe00554d92e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c9670-f49f-7559-a1e8-b1f1d40ac45d" xlink:to="loc_srt_MaximumMember_019c9670-f49f-72b6-8082-fbe00554d92e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019c9670-f49f-70e4-a66a-ca879e7c6196" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-75fa-b30e-496c84ccdd60" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019c9670-f49f-70e4-a66a-ca879e7c6196" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f49f-70e4-a66a-ca879e7c6196_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019c9670-f49f-70e4-a66a-ca879e7c6196" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f49f-70e4-a66a-ca879e7c6196_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f49f-7942-86ce-01d700a66eed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019c9670-f49f-70e4-a66a-ca879e7c6196" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f49f-7942-86ce-01d700a66eed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_019c9670-f49f-7bd0-b95a-faf8db44421e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c9670-f49f-7942-86ce-01d700a66eed" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_019c9670-f49f-7bd0-b95a-faf8db44421e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_RestructuringAndRelatedActivitiesEstimatedCompletionPeriod_019c9670-f49f-75e6-b17b-95c1b91dfb2a" xlink:href="alit-20260331.xsd#alit_RestructuringAndRelatedActivitiesEstimatedCompletionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-784e-96c6-0f2bada1a802" xlink:to="loc_alit_RestructuringAndRelatedActivitiesEstimatedCompletionPeriod_019c9670-f49f-75e6-b17b-95c1b91dfb2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_019c9670-f49f-72b4-bfe7-ba0eec58e4b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostCostIncurredToDate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-784e-96c6-0f2bada1a802" xlink:to="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_019c9670-f49f-72b4-bfe7-ba0eec58e4b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_019c9670-f49f-7dc0-9047-915754cab5e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-784e-96c6-0f2bada1a802" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_019c9670-f49f-7dc0-9047-915754cab5e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_RestructuringAndRelatedActivitiesEstimatedAnnualSavings_019c9670-f49f-71a0-9b3a-0dbfbbe6d296" xlink:href="alit-20260331.xsd#alit_RestructuringAndRelatedActivitiesEstimatedAnnualSavings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-784e-96c6-0f2bada1a802" xlink:to="loc_alit_RestructuringAndRelatedActivitiesEstimatedAnnualSavings_019c9670-f49f-71a0-9b3a-0dbfbbe6d296" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_019c9670-f49f-7f9f-bda4-1100001ecfce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-784e-96c6-0f2bada1a802" xlink:to="loc_us-gaap_RestructuringReserve_019c9670-f49f-7f9f-bda4-1100001ecfce" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/RestructuringSummaryofRestructuringCostsDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#RestructuringSummaryofRestructuringCostsDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/RestructuringSummaryofRestructuringCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-75f7-9b15-fc8d52f018d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-7822-aa7b-33a05974ff25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-75f7-9b15-fc8d52f018d1" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-7822-aa7b-33a05974ff25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-7a3a-9ce5-fdccc734a08d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-7822-aa7b-33a05974ff25" xlink:to="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-7a3a-9ce5-fdccc734a08d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7a3a-9ce5-fdccc734a08d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-7a3a-9ce5-fdccc734a08d" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7a3a-9ce5-fdccc734a08d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7802-a5ba-11daf45b293d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-7a3a-9ce5-fdccc734a08d" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7802-a5ba-11daf45b293d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TransformationProgramMember_019c9670-f49f-77a6-9013-28b4375aa448" xlink:href="alit-20260331.xsd#alit_TransformationProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7802-a5ba-11daf45b293d" xlink:to="loc_alit_TransformationProgramMember_019c9670-f49f-77a6-9013-28b4375aa448" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PostSeparationPlanMember_019c9670-f49f-7d18-8a48-e6887d5f155a" xlink:href="alit-20260331.xsd#alit_PostSeparationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7802-a5ba-11daf45b293d" xlink:to="loc_alit_PostSeparationPlanMember_019c9670-f49f-7d18-8a48-e6887d5f155a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7b55-9013-cf241a95ebd4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-7822-aa7b-33a05974ff25" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7b55-9013-cf241a95ebd4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7b55-9013-cf241a95ebd4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7b55-9013-cf241a95ebd4" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7b55-9013-cf241a95ebd4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7f22-8bb4-35dbfa65526b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7b55-9013-cf241a95ebd4" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7f22-8bb4-35dbfa65526b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_019c9670-f49f-74d9-b407-5e74e33cd32d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7f22-8bb4-35dbfa65526b" xlink:to="loc_us-gaap_EmployeeSeveranceMember_019c9670-f49f-74d9-b407-5e74e33cd32d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_019c9670-f49f-7fde-b0f9-ee98afbb5923" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7f22-8bb4-35dbfa65526b" xlink:to="loc_us-gaap_OtherRestructuringMember_019c9670-f49f-7fde-b0f9-ee98afbb5923" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCosts_019c9670-f49f-7d7b-be1c-c233f19ce74c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-75f7-9b15-fc8d52f018d1" xlink:to="loc_us-gaap_RestructuringCosts_019c9670-f49f-7d7b-be1c-c233f19ce74c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_019c9670-f49f-7981-a4f6-b40fa0f9ca15" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostCostIncurredToDate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-75f7-9b15-fc8d52f018d1" xlink:to="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_019c9670-f49f-7981-a4f6-b40fa0f9ca15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCostRemaining1_019c9670-f49f-7004-bd8f-545b2ee48c42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostExpectedCostRemaining1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-75f7-9b15-fc8d52f018d1" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCostRemaining1_019c9670-f49f-7004-bd8f-545b2ee48c42" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_019c9670-f49f-78e8-afdf-f17513516080" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-75f7-9b15-fc8d52f018d1" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_019c9670-f49f-78e8-afdf-f17513516080" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/RestructuringSummaryofRestructuringCostsFootnoteDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#RestructuringSummaryofRestructuringCostsFootnoteDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/RestructuringSummaryofRestructuringCostsFootnoteDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-7707-97c6-77cc7e81cefa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-775d-9a29-6451f8444845" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-7707-97c6-77cc7e81cefa" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-775d-9a29-6451f8444845" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-74de-b055-c4c2ff539181" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-775d-9a29-6451f8444845" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-74de-b055-c4c2ff539181" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-74de-b055-c4c2ff539181_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-74de-b055-c4c2ff539181" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-74de-b055-c4c2ff539181_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7341-ae0d-038c10aef69a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-74de-b055-c4c2ff539181" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7341-ae0d-038c10aef69a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_019c9670-f49f-792a-a0d0-9cc404405029" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7341-ae0d-038c10aef69a" xlink:to="loc_us-gaap_OtherRestructuringMember_019c9670-f49f-792a-a0d0-9cc404405029" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAmountOfLossRecoveryOnPlantAbandonment_019c9670-f49f-76b1-b98b-385153b08028" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAmountOfLossRecoveryOnPlantAbandonment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-7707-97c6-77cc7e81cefa" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAmountOfLossRecoveryOnPlantAbandonment_019c9670-f49f-76b1-b98b-385153b08028" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/RestructuringScheduleofAccruedRestructuringLiabilityDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#RestructuringScheduleofAccruedRestructuringLiabilityDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/RestructuringScheduleofAccruedRestructuringLiabilityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-7d88-9aeb-3a1f0b682beb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-78d9-bce3-0b29fb4f455b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-7d88-9aeb-3a1f0b682beb" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-78d9-bce3-0b29fb4f455b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-7184-8b7f-82609d174914" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-78d9-bce3-0b29fb4f455b" xlink:to="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-7184-8b7f-82609d174914" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7184-8b7f-82609d174914_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-7184-8b7f-82609d174914" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7184-8b7f-82609d174914_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7892-8ffb-deedbeba3520" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c9670-f49f-7184-8b7f-82609d174914" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7892-8ffb-deedbeba3520" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_TransformationProgramMember_019c9670-f49f-7618-852d-c933302da5be" xlink:href="alit-20260331.xsd#alit_TransformationProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7892-8ffb-deedbeba3520" xlink:to="loc_alit_TransformationProgramMember_019c9670-f49f-7618-852d-c933302da5be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PostSeparationPlanMember_019c9670-f49f-7299-99b4-6557f9ce4231" xlink:href="alit-20260331.xsd#alit_PostSeparationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c9670-f49f-7892-8ffb-deedbeba3520" xlink:to="loc_alit_PostSeparationPlanMember_019c9670-f49f-7299-99b4-6557f9ce4231" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7d9d-bd3f-b57138ba11d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c9670-f49f-78d9-bce3-0b29fb4f455b" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7d9d-bd3f-b57138ba11d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7d9d-bd3f-b57138ba11d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7d9d-bd3f-b57138ba11d3" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7d9d-bd3f-b57138ba11d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7962-bdfa-484668c2b767" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c9670-f49f-7d9d-bd3f-b57138ba11d3" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7962-bdfa-484668c2b767" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_019c9670-f49f-7202-aa3b-44f1d5f3347a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019c9670-f49f-7962-bdfa-484668c2b767" xlink:to="loc_us-gaap_EmployeeSeveranceMember_019c9670-f49f-7202-aa3b-44f1d5f3347a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_019c9670-f49f-764d-95c1-f88069710319" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c9670-f49f-7d88-9aeb-3a1f0b682beb" xlink:to="loc_us-gaap_RestructuringReserveRollForward_019c9670-f49f-764d-95c1-f88069710319" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_019c9670-f49f-7c96-b7e4-03af8ea6a845" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c9670-f49f-764d-95c1-f88069710319" xlink:to="loc_us-gaap_RestructuringReserve_019c9670-f49f-7c96-b7e4-03af8ea6a845" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_019c9670-f49f-76df-8f6b-fd7bf78e879b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c9670-f49f-764d-95c1-f88069710319" xlink:to="loc_us-gaap_RestructuringCharges_019c9670-f49f-76df-8f6b-fd7bf78e879b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_019c9670-f49f-7ac1-932f-6e079965c239" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c9670-f49f-764d-95c1-f88069710319" xlink:to="loc_us-gaap_PaymentsForRestructuring_019c9670-f49f-7ac1-932f-6e079965c239" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_019c9670-f49f-795e-8ece-e31ef4b02ea1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://alight.com/role/CommitmentsandContingenciesAdditionalInformationDetails" xlink:type="simple" xlink:href="alit-20260331.xsd#CommitmentsandContingenciesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://alight.com/role/CommitmentsandContingenciesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:href="alit-20260331.xsd#alit_CommitmentAndContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_CommitmentAndContingenciesTable_019c9670-f49f-7f98-a150-038c4a20effc" xlink:href="alit-20260331.xsd#alit_CommitmentAndContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_alit_CommitmentAndContingenciesTable_019c9670-f49f-7f98-a150-038c4a20effc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegistrationPaymentArrangementByArrangementAxis_019c9670-f49f-7e52-9146-d18d127eca3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegistrationPaymentArrangementByArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_alit_CommitmentAndContingenciesTable_019c9670-f49f-7f98-a150-038c4a20effc" xlink:to="loc_us-gaap_RegistrationPaymentArrangementByArrangementAxis_019c9670-f49f-7e52-9146-d18d127eca3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegistrationPaymentArrangementArrangementDomain_019c9670-f49f-7e52-9146-d18d127eca3e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegistrationPaymentArrangementArrangementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RegistrationPaymentArrangementByArrangementAxis_019c9670-f49f-7e52-9146-d18d127eca3e" xlink:to="loc_us-gaap_RegistrationPaymentArrangementArrangementDomain_019c9670-f49f-7e52-9146-d18d127eca3e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegistrationPaymentArrangementArrangementDomain_019c9670-f49f-7140-844b-4cf93307f39f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegistrationPaymentArrangementArrangementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RegistrationPaymentArrangementByArrangementAxis_019c9670-f49f-7e52-9146-d18d127eca3e" xlink:to="loc_us-gaap_RegistrationPaymentArrangementArrangementDomain_019c9670-f49f-7140-844b-4cf93307f39f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PurchaseObligationsMember_019c9670-f49f-7bde-bdb2-bcafce208705" xlink:href="alit-20260331.xsd#alit_PurchaseObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegistrationPaymentArrangementArrangementDomain_019c9670-f49f-7140-844b-4cf93307f39f" xlink:to="loc_alit_PurchaseObligationsMember_019c9670-f49f-7bde-bdb2-bcafce208705" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ServiceObligationMember_019c9670-f49f-7945-962c-876c88ccea73" xlink:href="alit-20260331.xsd#alit_ServiceObligationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RegistrationPaymentArrangementArrangementDomain_019c9670-f49f-7140-844b-4cf93307f39f" xlink:to="loc_alit_ServiceObligationMember_019c9670-f49f-7945-962c-876c88ccea73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligation_019c9670-f49f-7f12-aa84-e7e21d7d53b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_PurchaseObligation_019c9670-f49f-7f12-aa84-e7e21d7d53b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationTerm_019c9670-f49f-7ced-947f-7743a6f81c88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnrecordedUnconditionalPurchaseObligationTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationTerm_019c9670-f49f-7ced-947f-7743a6f81c88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear_019d4ef3-1470-79f7-83f6-10405a15f178" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear_019d4ef3-1470-79f7-83f6-10405a15f178" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_019c9670-f49f-79eb-ab6b-21c600124a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligationDueInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_019c9670-f49f-79eb-ab6b-21c600124a8e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInSecondYear_019c9670-f49f-7589-9a35-93f6b4b15776" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligationDueInSecondYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_PurchaseObligationDueInSecondYear_019c9670-f49f-7589-9a35-93f6b4b15776" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInThirdYear_019c9670-f49f-717e-a932-84960138e410" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligationDueInThirdYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_PurchaseObligationDueInThirdYear_019c9670-f49f-717e-a932-84960138e410" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_PurchaseObligationToBePaidAfterYearThree_019c9670-f49f-7265-9db1-421123eb1bab" xlink:href="alit-20260331.xsd#alit_PurchaseObligationToBePaidAfterYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_alit_PurchaseObligationToBePaidAfterYearThree_019c9670-f49f-7265-9db1-421123eb1bab" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligationFutureMinimumPaymentsDueRemainderOfFiscalYear_019d4ef5-5f56-7f99-b1d6-b39e58d48403" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractualObligationFutureMinimumPaymentsDueRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_ContractualObligationFutureMinimumPaymentsDueRemainderOfFiscalYear_019d4ef5-5f56-7f99-b1d6-b39e58d48403" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligationDueInNextTwelveMonths_019c9670-f49f-7db7-bacd-7f2ac6117101" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractualObligationDueInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_ContractualObligationDueInNextTwelveMonths_019c9670-f49f-7db7-bacd-7f2ac6117101" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligationDueInSecondYear_019c9670-f49f-7ccf-a5b3-b00437af6d91" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractualObligationDueInSecondYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_ContractualObligationDueInSecondYear_019c9670-f49f-7ccf-a5b3-b00437af6d91" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligationDueInThirdYear_019c9670-f49f-77b1-8047-61541d74f2fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractualObligationDueInThirdYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_ContractualObligationDueInThirdYear_019c9670-f49f-77b1-8047-61541d74f2fd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_alit_ContractualObligationToBePaidThereafter_019c9670-f49f-7f85-9d14-5c4caca38a5b" xlink:href="alit-20260331.xsd#alit_ContractualObligationToBePaidThereafter"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_alit_ContractualObligationToBePaidThereafter_019c9670-f49f-7f85-9d14-5c4caca38a5b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualObligation_019c9670-f49f-7139-91d2-4d019d53be6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractualObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_alit_CommitmentAndContingenciesLineItems_019c9670-f49f-7a2c-b01b-fd6f8f6bb0cb" xlink:to="loc_us-gaap_ContractualObligation_019c9670-f49f-7139-91d2-4d019d53be6c" xlink:type="arc" order="12"/>
  </link:definitionLink>
</link:linkbase>
