A bill to legalize gay marriage in Washington state won final legislative approval on Wednesday in a vote that moved the state one step closer to becoming the seventh to recognize same-sex nuptials.

Washington's Democratic Governor Christine Gregoire said she looked forward to signing the measure and "putting into law an end to an era of discrimination" even as opponents, led by religious conservatives, vowed to seek its repeal at the polls in November.

The approval in the state House of Representatives came a day after gay marriage advocates won a key legal victory in California when a federal appeals court declared a voter-approved gay marriage ban in that state unconstitutional.

The measure cleared the state House of Representatives 55-43, a week after it was passed by the state Senate by a 28-21 vote. Democrats, accounting for the lion's share of support for the bill, control both legislative bodies in the state capital Olympia but enjoy a bigger majority in the 98-seat House.

Two Republicans joined 53 Democrats in voting for the bill, while two Democrats sided with 41 Republicans in opposition.

Democratic Representative Jamie Pedersen, a gay lawmaker from Seattle who has sponsored gay rights bills in the House for several years, said domestic partnership laws, as the state has had for years, are "a pale and inadequate substitute for marriage".

Pedersen, during his remarks on the House floor, read from Tuesday's ruling by the San Francisco-based 9th US Circuit Court of Appeals, citing a section that stated "marriage is the name that society gives to the relationship that matters most between two adults".