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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019dfdfd-ad07-735f-b7b9-c4b2c7cb8101,g:2b40c5dd-9862-4250-8c18-00ad73f328de-->
<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/DocumentAndEntityInformation" xlink:type="simple" xlink:href="alit-20260803.xsd#DocumentAndEntityInformation"/>
  <link:definitionLink xlink:role="http://alight.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019fa8b3-eacb-7388-9974-269facb4c83f" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_DocumentInformationTable_019fa8b3-eacb-7388-9974-269facb4c83f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressesAddressTypeAxis_019fa8b4-6200-791d-80b9-31a49f8125a7" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressesAddressTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019fa8b3-eacb-7388-9974-269facb4c83f" xlink:to="loc_dei_EntityAddressesAddressTypeAxis_019fa8b4-6200-791d-80b9-31a49f8125a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AddressTypeDomain_019fa8b4-6200-791d-80b9-31a49f8125a7_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AddressTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityAddressesAddressTypeAxis_019fa8b4-6200-791d-80b9-31a49f8125a7" xlink:to="loc_dei_AddressTypeDomain_019fa8b4-6200-791d-80b9-31a49f8125a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AddressTypeDomain_019fa8b4-b3df-7f46-b5b8-c9e83960a3c5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AddressTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityAddressesAddressTypeAxis_019fa8b4-6200-791d-80b9-31a49f8125a7" xlink:to="loc_dei_AddressTypeDomain_019fa8b4-b3df-7f46-b5b8-c9e83960a3c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_FormerAddressMember_019fa8b5-1179-76dd-a75a-717c467ee8a0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_FormerAddressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_AddressTypeDomain_019fa8b4-b3df-7f46-b5b8-c9e83960a3c5" xlink:to="loc_dei_FormerAddressMember_019fa8b5-1179-76dd-a75a-717c467ee8a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019dfdfd-ad07-7e94-acbf-0f42a3f7507d" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityRegistrantName_019dfdfd-ad07-7e94-acbf-0f42a3f7507d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019dfdfd-ad07-7d97-ad63-3f842f19ee09" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_AmendmentFlag_019dfdfd-ad07-7d97-ad63-3f842f19ee09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019dfdfd-ad07-72f6-9580-64427eb689db" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityCentralIndexKey_019dfdfd-ad07-72f6-9580-64427eb689db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019dfdfd-ad07-7ba7-838a-5121a5715ced" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_DocumentType_019dfdfd-ad07-7ba7-838a-5121a5715ced" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019dfdfd-ad07-740c-9b94-23aca5f124ea" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_DocumentPeriodEndDate_019dfdfd-ad07-740c-9b94-23aca5f124ea" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019dfdfd-ad07-718f-a151-fd1d14e79fa3" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019dfdfd-ad07-718f-a151-fd1d14e79fa3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019dfdfd-ad07-7efc-a2bd-cb90622aa295" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityFileNumber_019dfdfd-ad07-7efc-a2bd-cb90622aa295" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019dfdfd-ad07-7220-81be-77182877a181" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityTaxIdentificationNumber_019dfdfd-ad07-7220-81be-77182877a181" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019dfdfd-ad07-7fae-ac2b-e71417243736" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityAddressAddressLine1_019dfdfd-ad07-7fae-ac2b-e71417243736" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019dfdfd-ad07-7216-a366-6dab7f1718d9" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityAddressAddressLine2_019dfdfd-ad07-7216-a366-6dab7f1718d9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine3_019dfdfd-ad07-794e-a007-0fb50c97f983" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityAddressAddressLine3_019dfdfd-ad07-794e-a007-0fb50c97f983" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019dfdfd-ad07-7a2b-b4f2-0631b6091827" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityAddressCityOrTown_019dfdfd-ad07-7a2b-b4f2-0631b6091827" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019dfdfd-ad07-7694-82f7-eb00cb834886" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityAddressStateOrProvince_019dfdfd-ad07-7694-82f7-eb00cb834886" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019dfdfd-ad07-749c-ac2c-7db7a5ae6977" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityAddressPostalZipCode_019dfdfd-ad07-749c-ac2c-7db7a5ae6977" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019dfdfd-ad07-7787-833c-f5c25a85a955" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_CityAreaCode_019dfdfd-ad07-7787-833c-f5c25a85a955" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019dfdfd-ad07-748c-912d-e17f2e3de164" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_LocalPhoneNumber_019dfdfd-ad07-748c-912d-e17f2e3de164" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019dfdfd-ad07-79ce-834d-db726e0f1e59" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_WrittenCommunications_019dfdfd-ad07-79ce-834d-db726e0f1e59" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019dfdfd-ad07-70a6-ba02-e83372389ce9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_SolicitingMaterial_019dfdfd-ad07-70a6-ba02-e83372389ce9" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019dfdfd-ad07-7396-a407-cf335a8edb3b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_PreCommencementTenderOffer_019dfdfd-ad07-7396-a407-cf335a8edb3b" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019dfdfd-ad07-7d5a-a41a-01ff7ccad7af" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019dfdfd-ad07-7d5a-a41a-01ff7ccad7af" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019dfdfd-ad07-7afc-bd2e-f2b5d1ce6bff" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_Security12bTitle_019dfdfd-ad07-7afc-bd2e-f2b5d1ce6bff" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019dfdfd-ad07-76cd-9478-a7bf004f9a4d" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_TradingSymbol_019dfdfd-ad07-76cd-9478-a7bf004f9a4d" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019dfdfd-ad07-742a-a62f-e65c2e0e96a2" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_SecurityExchangeName_019dfdfd-ad07-742a-a62f-e65c2e0e96a2" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019dfdfd-ad07-765e-a5fa-d5e3fb2eac10" 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_019dfdfd-ad07-771f-aeac-ae719ac20310" xlink:to="loc_dei_EntityEmergingGrowthCompany_019dfdfd-ad07-765e-a5fa-d5e3fb2eac10" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
