The US Presbyterian Church has voted to allow clergy to perform same-sex weddings, in a reversal for one of the largest mainline Protestant denominations.
The move came during a meeting in Detroit, two years after the church's highest judicial body upheld a rebuke against a lesbian minister for officiating at same-sex weddings in California.
Several Christian denominations in the US have grappled in recent years with how to address the wishes of gay couples to marry, which is now legal in 19 states and the District of Columbia.
The Presbyterian Church in 2011 removed its prohibitions on openly gay clergy and has a long tradition of baptising children of same-sex couples.
The vote by a group of church elders and ministers to allow clergy to solemnise gay weddings was 371 in favour and 238 opposed, said Gradye Parsons, clerk of the church's general assembly.
The new rules, which take effect today, give clergy the choice of whether to preside over same-sex marriages in states where gay nuptials were legally recognised, while providing church councils with discretion over whether to host such ceremonies.
The church previously only permitted its ministers to bless unions between two men or two women so long as pastors did not state or imply the pair were actually being married.
The same body in Detroit also voted to change the language of the church's Book of Order to state: "Marriage involves a unique commitment between two people, traditionally between a man and a woman."
The original passage says: "Marriage is a civil contract between a man and a woman."
That change would require the approval of local church leaders and would take at least a year to come into force, Parsons said.
The Presbyterian denomination had more than 1.7 million active members last year.
The church has lost more than 500,000 members over the past decade, and leaders have expressed concern that an endorsement of same-sex marriage could spur an exodus of parishioners who viewed it as incompatible with biblical teachings.
The church's general assembly in July 2012 narrowly voted to reject a proposal to redefine marriage as a union between "two people" rather than as between a man and a woman.
The United Methodist Church, the nation's largest mainline Protestant denomination, still forbids gay marriage.