Gay rights supporters in neighboring Oregon said the passage of same-sex marriage measures in other states gives them hope for 2014.
Domestic partnerships are legal in Oregon, but same-sex marriage was banned by ballot measure in 2004.
Jeana Frazzini, director of the gay-rights group Basic Rights Oregon, said they considered going to the ballot to overturn the constitutional amendment this year but abandoned the effort in part because there wasn't clear evidence it could pass.
"Basic Rights Oregon is committed to leading the way to make Oregon the first state to overturn a constitutional amendment banning marriage," she said in statement.
Gay couples in Washington could start picking up their marriage certificates and licenses from county auditor offices Dec. 6, a day after the election is certified. However, because Washington has a three-day waiting period, the earliest a certificate could be signed, making the marriage valid, is Dec. 9.
The law doesn't require religious organizations or churches to perform marriages, and it doesn't subject churches to penalties if they don't marry gay or lesbian couples.
The path to gay marriage in Washington state began several years ago.
A 2006 state Supreme Court ruling upheld a 1998 law banning same-sex marriage. But earlier that year, a gay civil rights measure passed after the idea had failed for nearly 30 years, signaling a change of mindset in the Legislature.
The state's first domestic partnership law passed in 2007, granting couples about two dozen rights, including hospital visitation and inheritance rights when there is no will. It was expanded a year later, and then again in 2009, when lawmakers completed the package with the so-called "everything but marriage" law that was ultimately upheld by voters later that year.
This year, lawmakers passed the law allowing gay marriage, and Gregoire signed it in February. Preserve Marriage gathered enough signatures for a referendum, putting the law on hold before it could take effect.
State Sen. Ed Murray, a Democratic gay lawmaker from Seattle, sponsored the law. He said the election's outcome "rectifies an injustice that was done to gay and lesbian couples" when the state Legislature passed the Defense of Marriage Act banning gay marriage in the state.
Murray was in his third year as a state representative when that 1998 law passed. At the time, he was the Legislature's lone gay lawmaker.
"I believe that when the marriages start happening next month, that will be a healing moment for this state," he said.
AP writer Jonathan J. Cooper contributed from Portland, Ore. Follow Rachel La Corte at http://www.twitter.com/RachelAPOly or http://www.facebook.com/news.rachel