<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.unitedcontinentalholdings.com/role/DocumentAndEntityInformation" xlink:href="ual-20200106.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.unitedcontinentalholdings.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityInformationLineItems" xlink:label="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:type="locator" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntitiesTable" xlink:label="loc_dei_EntitiesTable_5590B07B4ECAABEF63636D28BBB6A56B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntitiesTable_5590B07B4ECAABEF63636D28BBB6A56B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_DB1F4A4DF03308F2EFF16D28BBB6A6B6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_5590B07B4ECAABEF63636D28BBB6A56B" xlink:to="loc_dei_LegalEntityAxis_DB1F4A4DF03308F2EFF16D28BBB6A6B6" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_451FAC5B81BE13E2DFB16D28BBB66FF7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_DB1F4A4DF03308F2EFF16D28BBB6A6B6" xlink:to="loc_dei_EntityDomain_451FAC5B81BE13E2DFB16D28BBB66FF7_default" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_451FAC5B81BE13E2DFB16D28BBB66FF7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_DB1F4A4DF03308F2EFF16D28BBB6A6B6" xlink:to="loc_dei_EntityDomain_451FAC5B81BE13E2DFB16D28BBB66FF7" xlink:type="arc" />
    <link:loc xlink:href="ual-20200106.xsd#ual_UnitedAirLinesIncMember" xlink:label="loc_ual_UnitedAirLinesIncMember_6C85B356A274160556C26D28BBB63E67" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_451FAC5B81BE13E2DFB16D28BBB66FF7" xlink:to="loc_ual_UnitedAirLinesIncMember_6C85B356A274160556C26D28BBB63E67" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentType" xlink:label="loc_dei_DocumentType_F9D1EF71310039923BC66D28BBB6D9CB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_DocumentType_F9D1EF71310039923BC66D28BBB6D9CB" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_AmendmentFlag" xlink:label="loc_dei_AmendmentFlag_6ECFF0C1C327099B30446D28BBB67FF5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_AmendmentFlag_6ECFF0C1C327099B30446D28BBB67FF5" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="loc_dei_DocumentPeriodEndDate_1B59F9B1E645130FE9BC6D28BBB6D146" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_DocumentPeriodEndDate_1B59F9B1E645130FE9BC6D28BBB6D146" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityRegistrantName" xlink:label="loc_dei_EntityRegistrantName_CD9B83EFDED4B43147966D28BBB6E790" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityRegistrantName_CD9B83EFDED4B43147966D28BBB6E790" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="loc_dei_EntityCentralIndexKey_F71FE0F737E1DE86D9336D28BBB6078B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityCentralIndexKey_F71FE0F737E1DE86D9336D28BBB6078B" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityIncorporationStateCountryCode" xlink:label="loc_dei_EntityIncorporationStateCountryCode_7010B532848612639C926D28BBB60131" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityIncorporationStateCountryCode_7010B532848612639C926D28BBB60131" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFileNumber" xlink:label="loc_dei_EntityFileNumber_D069EF96AF3E0C0C7A5C6D28BBB67B9E" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityFileNumber_D069EF96AF3E0C0C7A5C6D28BBB67B9E" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityTaxIdentificationNumber" xlink:label="loc_dei_EntityTaxIdentificationNumber_B2C4CD1CA1507DDCF7136D28BBC59627" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityTaxIdentificationNumber_B2C4CD1CA1507DDCF7136D28BBC59627" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressAddressLine1" xlink:label="loc_dei_EntityAddressAddressLine1_5C5F908DF4B57F39AB706D28BBC513D8" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityAddressAddressLine1_5C5F908DF4B57F39AB706D28BBC513D8" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressCityOrTown" xlink:label="loc_dei_EntityAddressCityOrTown_F29DAA09EF3D2ADC44D26D28BBC54736" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityAddressCityOrTown_F29DAA09EF3D2ADC44D26D28BBC54736" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressStateOrProvince" xlink:label="loc_dei_EntityAddressStateOrProvince_46224576888C3CB529FE6D28BBC5C419" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityAddressStateOrProvince_46224576888C3CB529FE6D28BBC5C419" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressPostalZipCode" xlink:label="loc_dei_EntityAddressPostalZipCode_C7963671B699885A6AB56D28BBC5BB71" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityAddressPostalZipCode_C7963671B699885A6AB56D28BBC5BB71" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CityAreaCode" xlink:label="loc_dei_CityAreaCode_51E424DB594E0B9866E76D28BBC59DB5" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_CityAreaCode_51E424DB594E0B9866E76D28BBC59DB5" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LocalPhoneNumber" xlink:label="loc_dei_LocalPhoneNumber_48CEA08C3C6E0B4440E36D28BBC5A334" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_LocalPhoneNumber_48CEA08C3C6E0B4440E36D28BBC5A334" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_WrittenCommunications" xlink:label="loc_dei_WrittenCommunications_B94AD7F068CABA01286A6D28BBC50C61" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_WrittenCommunications_B94AD7F068CABA01286A6D28BBC50C61" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_SolicitingMaterial" xlink:label="loc_dei_SolicitingMaterial_92B64AE51CA84B8FD3E56D28BBC5F961" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_SolicitingMaterial_92B64AE51CA84B8FD3E56D28BBC5F961" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_PreCommencementTenderOffer" xlink:label="loc_dei_PreCommencementTenderOffer_834695AF202B617B58B56D28BBC558B4" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_PreCommencementTenderOffer_834695AF202B617B58B56D28BBC558B4" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_PreCommencementIssuerTenderOffer" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_8657197B6B8BEC74ACE36D28BBC56EEB" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_8657197B6B8BEC74ACE36D28BBC56EEB" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_Security12bTitle" xlink:label="loc_dei_Security12bTitle_29670575663F1DCBA25B6D28BBC51FEE" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_Security12bTitle_29670575663F1DCBA25B6D28BBC51FEE" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_TradingSymbol" xlink:label="loc_dei_TradingSymbol_97098D0EF6E2DF78A7D76D28BBC50036" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_TradingSymbol_97098D0EF6E2DF78A7D76D28BBC50036" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_SecurityExchangeName" xlink:label="loc_dei_SecurityExchangeName_B892552CEA4D47D8FE1A6D28BBC5BD0D" xlink:type="locator" />
    <link:definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_SecurityExchangeName_B892552CEA4D47D8FE1A6D28BBC5BD0D" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityEmergingGrowthCompany" xlink:label="loc_dei_EntityEmergingGrowthCompany_303977505D70B7FAA9866D28BBC5CA5D" xlink:type="locator" />
    <link:definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_C0CF115DFFDAD13AC2DF6D28BBB6CF29" xlink:to="loc_dei_EntityEmergingGrowthCompany_303977505D70B7FAA9866D28BBC5CA5D" xlink:type="arc" />
  </link:definitionLink>
</link:linkbase>
