Washington DC’s mayor Adrian Fenty has signed a bill allowing gay marriage in the district.
He signed it at a public ceremony at All Souls Church, which has a gay-friendly Unitarian congregation.
It does not automatically come into law.
Instead, it must undergo a 30-day Congressional review. If no complaints are lodged, it is expected gay couples can begin to marry in March.
The Washington DC council voted 11-2 to pass the bill on Tuesday.
The move will make DC the sixth US state to grant full marriage equality to gays and lesbians.
Massachusetts, Vermont, Iowa and Connecticut already allow gay marriage and New Hampshire will join them next month.
California voters repealed the right last November, while Maine voters struck down a law this autumn which would allowed same-sex marriages.