As predicted, the Washington DC council has voted 11-2 to legalise gay marriage in the district on Tuesday.
Mayor Adrian Fenty has promised to sign the bill when it reaches his desk, which is the next stage.
It will then be subject to a 30-day Congressional review and if no complaints are lodged, will become law.
The Democratic-controlled Congress could veto the bill, but is thought to be reluctant to do so.
If the bill passes Congress, it will allow gay couples to begin marrying in March.
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California voters repealed the right last November, while Maine voters struck down a law this autumn which would allowed same-sex marriages.