MPs have supported David Cameron's plan to allow gay marriage by a majority of 225, despite an estimated 136 Tories voting against the bill.
Party leaders hailed the decision by 400 votes to 175, to give the Marriage (Same Sex Couples) Bill a second reading as a "landmark" in the fight for equality.
But the bill still faces hurdles as it moves into the committee stage and on to the House of Lords after a number of prominent Tories argued the move would undermine marriage, alienate voters and damage the party's election prospects.
Former minister Tim Loughton told Sky News after the vote that the opposition, which was greater than the number of Tories who backed the bill, was not about Mr Cameron's leadership.
"It is all about a conscience issue about gay marriages where many of us have very considerable concerns about the nature of this legislation, the flaws in this legislation and what it is trying to do.
"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."
More than 50 Tory MPs later rebelled in a whipped vote on the timetable for the bill. Many backbenchers said they believed it should be scrutinised by the House rather than a committee of MPs.
Responding to the vote on Twitter, Mr Cameron 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."
Less than two hours before the ballot, he had recorded a statement reiterating that he is a "strong believer" in the issue.
"This is, yes, about equality. But it is also about making our society stronger," he said.
The proposed bill would 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 would also allow couples who had previously entered into civil partnerships to convert their relationship into a marriage.