Washington D.C. Mayor Adrian Fenty signed a bill Friday to legalize same sex marriage at the All Souls Unitarian Church.
The D.C. City Council approved the measure last week. But Congress still has to sign off on it.
It must pass a 30-day period of congressional review.
Gay couples could begin marrying in the district as early as March. However, opponents vow to fight the law.
As of right now, Connecticut, Iowa, New Hampshire, and Vermont, and Massachusetts are the only states to have legalized same-sex marriage.