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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-09-27</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001543418</issuerCik>
        <issuerName>Trilogy Metals Inc.</issuerName>
        <issuerTradingSymbol>TMQ</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001035674</rptOwnerCik>
            <rptOwnerName>PAULSON &amp; CO. INC.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1251 AVENUE OF THE AMERICAS</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10020</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 Shares, no par value</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </securityTitle>
            <transactionDate>
                <value>2016-09-27</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>10400</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.5594</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11613051</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Managed Funds and Accounts</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Shares, no par value</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </securityTitle>
            <transactionDate>
                <value>2016-09-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>773</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.5503</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11612278</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Managed Funds and Accounts</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Paulson &amp; Co. Inc. (&quot;Paulson&quot;) is an investment advisor registered under the Investment Advisors Act of 1940. Paulson is the investment manager of investment funds (the &quot;Funds&quot;) and certain separately managed accounts (the &quot;Separately Managed Accounts&quot;). John Paulson is the controlling person of Paulson. All securities reported on this Form 4 are owned by the Funds or held in the Separately Managed Accounts.</footnote>
        <footnote id="F2">Each of Paulson and John Paulson may be deemed to indirectly beneficially own the securities directly owned by the Funds or held in the Separately Managed Accounts. Pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, as amended (the &quot;Act&quot;), the filing of this Form 4 shall not be deemed an admission by any person reporting on this Form 4 that such person, for purposes of Section 16 of the Act or otherwise, is the beneficial owner of any equity securities covered by this Form 4.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Stuart L. Merzer, General Counsel &amp; Chief Compliance Officer for Paulson &amp; Co. Inc.</signatureName>
        <signatureDate>2016-09-29</signatureDate>
    </ownerSignature>
</ownershipDocument>
