David Cameron has succeeded in pushing through plans for gay marriage but his party has been torn in two by the controversial move.
The Prime Minister hailed the vote, which was won by a big margin of 400 to 175 - a majority of 225, as a "step forward for our country".
But he is facing deep divisions after 136 Tories including two Cabinet ministers - more than half the party - took advantage of the free vote to vote against.
Conservative Stewart Jackson wrote on Twitter: "David Cameron has split the Conservative Party in half on gay marriage and failed to win a majority of Tory MPs. Labour win."
Just 127 Conservatives endorsed the Marriage (Same Sex Couples) Bill at its second reading, with 40 more either formally abstaining or not voting.
Environment Secretary Owen Paterson and Welsh Secretary David Jones voted against, while Defence Secretary Philip Hammond and Attorney General Dominic Grieve stayed away.
There was one boost for Downing Street because no Government members quit to join a rebellion over a whipped vote on the timetable for the bill.
But more than 50 Tories did vote against the timetable, arguing that the proposals should be scrutinised by the House rather than a committee of MPs.
Mr Cameron, writing on Twitter after the vote, said: "Strong views exist on both sides but I believe MPs voting for gay people being able to marry too, is a step forward for our country."
Labour leader Ed Miliband - who saw 22 of his own MPs vote against the new law - said it was a "proud day".
"The overwhelming majority of Labour MPs supported this change to make sure marriage reflects the value we place on long-term, loving relationships whoever you love," he said.
Deputy Prime Minister Nick Clegg - who saw four of his 56 MPs vote against, including ex-minister Sarah Teather - said it was a "landmark for equality".
"Marriage is about love and commitment and it should no longer be denied to people just because they are gay," he said.
The bill still faces hurdles as it moves into the committee stage and onto the House of Lords, where opponents are expected to mount tough resistance.
Former minister Tim Loughton told Sky News: "This is only the start of it, this has got may months to go through Parliament, but for the moment clearly they have got problems."
The result came after more than six hours of stormy debate. Mr Cameron sparked irritation by turning up for the vote but not speaking in the Commons.
Damage to his leadership was limited by his decision to offer Tories a free vote but the decision to force through the plans could fester.
Mr Jackson said: "The only comparable rebellion is the Iraq war vote in 2003 which undermined Blair's premiership. This vote will do the same for Cameron."
The legislation will allow same-sex couples to wed in both civil and religious ceremonies, provided that the religious institution consents.
Officials have stressed that religious organisations can decide for themselves if they want to "opt in" to holding gay weddings.
However, the Church of England is barred from performing such ceremonies unless it changes its laws.
The bill will also allow couples who had previously entered into civil partnerships to convert their relationship into a marriage.