|Governor Christine Gregoire (L) congratulates representative Jamie Pederson after the house passed the bill [Reuters]
Washington legislators have voted in favour of a bill legalising same-sex marriage, which should soon be signed into law by the governor, officials said.
The bill was passed by 55 votes to 43 in the lower-house House of Representatives, having already been approved by state senators last week.
Christine Gregoire, the state governor, has five days to approve the text, which would make Washington the seventh state in the US to allow gay marriage. The law would then go into effect 90 days later.
The governor said last month she supported the bill and that she planned to sign it if approved by legislators.
Six US states - Connecticut, Iowa, Massachusetts, New Hampshire, New York and Vermont - plus the District of Columbia already allow same-sex marriage, but the issue remains highly controversial.
The vote in Washington state comes a day after a US federal appeals court struck down a California law that had stripped gay couples of the right to marry.
Gay marriage was briefly authorised in California in 2008, but later banned by a referendum on what was known as Proposition 8. It rewrote the state's constitution to restrict marriage to unions between a man and a woman.
On Tuesday, the three-judge appeals panel in San Francisco ruled 2-1 that a lower court had properly declared the ban a violation of the US constitution.
But opponents of the legislation say they will try to gather enough signatures to call a public referendum on banning it in November. If they were to get the signatures needed, the law would be suspended until the referendum.