<SUBMISSION>
<ACCESSION-NUMBER>0001179110-16-016871
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20151231
<FILING-DATE>20160104
<DATE-OF-FILING-DATE-CHANGE>20160104
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>ATLANTIC POWER CORP
<CIK>0001419242
<ASSIGNED-SIC>4900
<IRS-NUMBER>550886410
<STATE-OF-INCORPORATION>A1
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>3 ALLIED DRIVE
<STREET2>SUITE 220
<CITY>DEDHAM
<STATE>MA
<ZIP>02026
<PHONE>617-977-2400
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>3 ALLIED DRIVE
<STREET2>SUITE 220
<CITY>DEDHAM
<STATE>MA
<ZIP>02026
</MAIL-ADDRESS>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>Ladhani Holli C.
<CIK>0001221455
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-34691
<FILM-NUMBER>161317474
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>2800 POST OAK BLVD.
<STREET2>SUITE 4500
<CITY>HOUSTON
<STATE>TX
<ZIP>77056
</MAIL-ADDRESS>
<FORMER-NAME>
<FORMER-CONFORMED-NAME>NICHOLS HOLLI
<DATE-CHANGED>20030303
</FORMER-NAME>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-12-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001419242</issuerCik>
        <issuerName>ATLANTIC POWER CORP</issuerName>
        <issuerTradingSymbol>AT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001221455</rptOwnerCik>
            <rptOwnerName>Ladhani Holli C.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ATLANTIC POWER CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>3 ALLIED DRIVE, SUITE 220</rptOwnerStreet2>
            <rptOwnerCity>DEDHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02026</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Deferred share units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2015-12-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>9981</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.69</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9981</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>95771</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Dividend equivalent rights accrued on the deferred share units granted under the Company's Deferred Share Unit Plan, which provides for the payment of all accrued deferred share units and dividend equivalent rights to the reporting person following his or her termination as a director. Each deferred share unit and each dividend equivalent right is equal to the economic equivalent of one common share.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s John S. Miele, attorney-in-fact</signatureName>
        <signatureDate>2016-01-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
