The nation's high court rejected an Arkansas law that treated gays differently from heterosexuals, overturning a state Supreme Court ruling that upheld the state statute.
Monday's 6-3 ruling was handed down on the second anniversary of the Obergefell v. Hodges decision, which struck down state bans on same-sex marriage by a 5-4 vote.
The court reached its decision in a summary reversal, opting not to hear oral arguments or request lengthy legal briefs before ruling.