British lawmakers voted in favour of legislation allowing gay marriage on Tuesday despite a split in Prime Minister David Cameron's Conservative party.
Members of parliament voted by 400 to 175 to approve the draft law allowing same-sex couples to marry in England and Wales.
In a late intervention just two hours before lawmakers voted, Cameron made a televised statement to say the move was about "making our society stronger".
But Conservative opponents to the bill had spoken out angrily in the debate before the vote, arguing that they undermined marriage and could damage the party's prospects at the next general election in 2015.
There was never any doubt that the legislation would pass because it had overwhelming support from the opposition Labour Party, so the key question was how many Conservative MPs would vote against.
Early estimates put the number of Tories who voted against their leader at between 140 and 150, or around half the Conservative lawmakers in the House of Commons.