The Minnesota Senate is expected to give final approval on Monday to a bill that would make the state the 12th in the United States to allow same-sex couples to marry and only the second in the Midwest.
Leaders in the Senate, where Democrats hold a 39-28 majority, have said they believe they have the support to approve a bill legalizing gay marriage. They set a vote for Monday on the measure that members of the state House approved last week.
Democratic Governor Mark Dayton has said he would sign the bill, which would make Minnesota the third state this month to legalize gay marriage after Rhode Island and Delaware. The law would take effect August 1.
Minnesota would join Iowa as the only other Midwestern state to permit gay marriage and the first to do so through legislation. Iowa has permitted same-sex marriage since 2009 under a state Supreme Court order.
The Minnesota House had been expected to be the bigger hurdle, but representatives voted 75-59 on Thursday to approve a bill with some Republican support.
The measure has at least one Republican sponsor in the Senate.
Senator Scott Dibble, the bill's architect, has said the stronger-than-expected vote from representatives was very encouraging and urged same-sex marriage supporters to continue active lobbying for the bill right up to Monday's vote.
Hundreds of supporters and opponents of the proposal to legalize same-sex marriage demonstrated at the Capitol on Thursday. A similar atmosphere was expected on Monday.
The vote on Thursday was a sharp reversal for Minnesota's legislature. Two years ago, Republicans controlled both chambers and bypassed the governor to put forward a ballot measure that would have made the state's current ban on gay marriage part of the state constitution.
Minnesota voters in November rejected that measure and also voted in Democratic majorities in both the state House and Senate, setting the legislature on the path toward Monday's vote.
Republican Senator Warren Limmer, a sponsor of the proposed amendment two years ago, has said the legislation will change how businesses work, clergy speak from the pulpit and school curriculums are shaped.
"Prior to the marriage amendment (vote) in November, many people were warning that this day would come," Limmer said in an interview last week.
Opponents of the bill have questioned whether the rights of religious groups and individuals who believe marriage should be only between one man and one woman would be protected. They also questioned the speed with which the measure was being approved.
Over several years, voters in more than two dozen states approved state constitutional provisions that define marriage as a union between a man and a woman. But in the past year, gay rights advocates won a series of victories.
In November, Maine, Maryland and Washington state became the first states to approve same-sex marriage at the ballot box.
Same-sex marriage is also legal in Massachusetts, Connecticut, New York, Vermont and New Hampshire. The District of Columbia also has legalized same-sex marriage.
Illinois state senators approved a bill in February, but the measure has not been voted on in the full House.