<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-02-26</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001095996</issuerCik>
        <issuerName>WILLIAM LYON HOMES</issuerName>
        <issuerTradingSymbol>WLH</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001316580</rptOwnerCik>
            <rptOwnerName>Luxor Capital Group, LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1114 AVENUE OF THE AMERICAS</rptOwnerStreet1>
            <rptOwnerStreet2>29TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10036</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001356913</rptOwnerCik>
            <rptOwnerName>LUXOR CAPITAL PARTNERS OFFSHORE LTD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O M&amp;C CORPORATE SVCS LTD</rptOwnerStreet1>
            <rptOwnerStreet2>PO BOX 309 GT UGLAND HOUSE</rptOwnerStreet2>
            <rptOwnerCity>GEORGE TOWN</rptOwnerCity>
            <rptOwnerState>E9</rptOwnerState>
            <rptOwnerZipCode>00000</rptOwnerZipCode>
            <rptOwnerStateDescription>CAYMAN ISLANDS</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001393021</rptOwnerCik>
            <rptOwnerName>Luxor Capital Partners, LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1114 AVENUE OF THE AMERICAS</rptOwnerStreet1>
            <rptOwnerStreet2>29TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10036</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001479129</rptOwnerCik>
            <rptOwnerName>Luxor Wavefront, LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1114 AVENUE OF THE AMERICAS</rptOwnerStreet1>
            <rptOwnerStreet2>29TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10036</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001270742</rptOwnerCik>
            <rptOwnerName>LCG HOLDINGS LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1114 AVENUE OF THE AMERICAS</rptOwnerStreet1>
            <rptOwnerStreet2>29TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10036</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common stock, Class A, par value $0.01</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2015-02-26</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>278780</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.5800</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1951466</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Luxor Capital Partners, LP</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common stock, Class A, par value $0.01</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2015-02-26</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>259280</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.5800</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>391175</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Luxor Wavefront, LP</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common stock, Class A, par value $0.01</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2015-02-26</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1230000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.5800</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1978215</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Luxor Capital II Company LLC</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common stock, Class A, par value $0.01</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2015-02-26</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>131940</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.5800</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>73932</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F5"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Separately Managed Account</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This Form 4 is filed jointly by Luxor Capital Group, LP (&quot;Luxor Capital Group&quot;), Luxor Capital Partners, LP (&quot;Onshore Fund&quot;), Luxor Capital Partners Offshore, Ltd. (&quot;Offshore Feeder Fund&quot;), Luxor Wavefront, LP (&quot;Wavefront Fund&quot;), LCG Holdings, LLC (&quot;LCG Holdings&quot;), Luxor Management, LLC (&quot;Luxor Management&quot;) and Christian Leone (collectively, the &quot;Reporting Persons&quot;).  Each of the Reporting Persons may be deemed to be a member of a Section 13(d) group that collectively owns more than 10% of the Issuer's outstanding shares of Common Stock. Each of the Reporting Persons disclaims beneficial ownership of the shares of Common Stock reported herein except to the extent of his or its pecuniary interest therein.</footnote>
        <footnote id="F2">Shares owned directly by Onshore Fund.  Each of LCG Holdings and Luxor Capital Group, as the general partner and investment manager, respectively, of Onshore Fund, may be deemed to beneficially own the shares of Common Stock owned directly by Onshore Fund.  Luxor Management, as the general partner of Luxor Capital Group, and Christian Leone, as the managing member of each of LCG Holdings and Luxor Management, may be deemed to beneficially own the shares of Common Stock owned directly by Onshore Fund.</footnote>
        <footnote id="F3">Shares owned directly by Wavefront Fund.  Each of LCG Holdings and Luxor Capital Group, as the general partner and investment manager, respectively, of Wavefront Fund, may be deemed to beneficially own the shares of Common Stock owned directly by Wavefront Fund.  Luxor Management, as the general partner of Luxor Capital Group, and Christian Leone, as the managing member of each of LCG Holdings and Luxor Management, may be deemed to beneficially own the shares of Common Stock owned directly by Wavefront Fund.</footnote>
        <footnote id="F4">Shares owned directly by Luxor Capital II Company LLC (&quot;Capital II&quot;). Each of  Luxor Capital II Company (&quot;Capital II Company&quot;), as the owner of a controlling interest in Capital II, Luxor Capital Partners Offshore Master Fund, LP (&quot;Offshore Master Fund&quot;), as the owner of a controlling interest in Capital II Company, and Offshore Feeder Fund,  as the owner of a controlling interest in Offshore Master Fund, may be deemed to beneficially own the shares of Common Stock owned directly by Capital II.  Each of LCG Holdings and Luxor Capital Group, as the general partner and investment manager, respectively, of Offshore Master Fund, may be deemed to beneficially own the shares of Common Stock owned directly by Capital II.  Luxor Management, as the general partner of Luxor Capital Group, and Christian Leone, as the managing member of each of LCG Holdings and Luxor Management, may be deemed to beneficially own the shares of Common Stock owned directly by Capital II.</footnote>
        <footnote id="F5">Shares held in an account separately managed by Luxor Capital Group (the &quot;Separately Managed Account&quot;).  Luxor Capital Group, as the investment manager of the Separately Managed Account, may be deemed to beneficially own the shares of Common Stock held in the Separately Managed Account.  Luxor Management, as the general partner of Luxor Capital Group, and Christian Leone, as the managing member of Luxor Management, may be deemed to beneficially own the shares of Common Stock held in the Separately Managed Account.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Norris Nissim, as General Counsel of Luxor Management, LLC, General Partner of Luxor Capital Group, LP</signatureName>
        <signatureDate>2015-03-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
