The Democratic-controlled House approved the Senate-passed measure on a mostly party-line 62-35 vote after nearly two hours of debate. It next goes to Gov. Chris Gregoire, who said she will sign it into law.
"Our state is one that thrives on diversity," Gregoire, a Democrat, said in a statement. "We have to respect and protect all of the families that make up our communities."
The bill expands on previous domestic partnership laws by adding reference to partnerships alongside all remaining areas of state law where currently only married couples are mentioned. The statutes range from labor and employment rights to pensions and other public employee benefits.
Conservatives are responding to it as (unsurprisingly) a threat to marriage.