Washington's gay marriage bill cleared the Senate late Wednesday night, moving the state closer to becoming the seventh to legalize same-sex marriage.
The 28-21 vote in favor of the measure sent it forward to Washington state's House of Representatives, where the bill is expected to win approval by a comfortable margin as early as next week, Reuters reported.
Both the Senate and the House in Washington are controlled by the Democrats. Four Republicans crossed party lines and voted to pass the bill, while three Democrats voted against it, the Associated Press reported. The public galleries burst into applause as the Senate passed the measure after over an hour of debate that was both emotional and respectful, lawmakers said.
"I believe an adult should be able to marry the person they love: It's that simple for me," said Sen. Steve Litzow, a first-term Republican, who was one of the four to support marriage equality, the Seattle Post-Intelligencer reported.
More from GlobalPost: Washington state lawmakers have the votes to legalize gay marriage
The bill's chief Senate sponsor, Democrat Ed Murray, said the votes were "a pleasant surprise," according to Reuters.
"I'm sincerely moved by my colleagues' courage, no matter how they voted," said Murray, who is gay.
He told colleagues on the floor before the vote that he looked forward to marrying his partner of more than 20 years and said Senate members should all expect an invitation in the mail, regardless of how they voted, Reuters reported.
Washington's Governor Chris Gregoire supports the same-sex marriage bill, and has said she will sign it into law, the AP reported.
More from GlobalPost: Gregoire pushes to legalize same-sex marriage in Washington
However, opponents have promised to repeal it with a referendum. In order to do so, they need to collect at least 120,577 signatures from registered voters by July 6 to qualify for the November ballot, Reuters reported.
Washington will join New York, Massachusetts, Connecticut, Vermont, New Hampshire, Iowa and the District of Columbia in their legalization of gay marriage. Similar laws are gaining support in Maryland and New Jersey as well, according to Reuters. A referendum to legalize gay marriage in Maine has also qualified for the state's November ballot.
More from GlobalPost: Microsoft, Starbucks support gay marriage in Washington
The Washington Poll, which has measured rapid opinion changes in the state over the past six years, found that 55 percent of Washingtonians said they would vote to sustain same-sex marriage if passed by the Legislature, The Post-Intelligencer reported.