Washington joins six other states and the District of Columbia in allowing same-sex marriage -- and the first state to strike down a law defining marriage as between one man and one woman, The Seattle Times reported.
"This is a very proud moment," Gregoire said. "It's a day that historians will mark as a milestone for equal rights in this state, a day when we did what was right ... just and fair. We did it together, Republicans and Democrats, gay and straight, young and old."
The legislation will not authorize same-sex marriage right away because changes in the state law will not take effect until June 7, one day after the state holds its 2012 primary. Opponents of same-sex marriage filed a referendum Monday and must collect 120,577 valid signatures on a petition to put the matter before voters, the newspaper said.
If the petition drive fails to get enough signatures for a June 6 referendum, the measure could go on the November ballot.
The bill signing in Olympia, Wash., took place the same day as the New Jersey state Senate voted 24-16 to legalize same-sex marriage. The state assembly is scheduled to take up the measure Thursday.
Gov. Chris Christie has vowed to veto the bill if it passes, and has said he wants to put the issue to a referendum in November, the (Newark) Star-Ledger reported.