MPs have voted 400 to 175 in supporting the government’s Marriage (Same Sex Couples) Bill - a majority of 225 votes - following an afternoon of heated debate in the House of Commons.
About 140 Conservative MPs are thought to have voted against the plans.
Former children’s minister and Conservative MP Tim Loughton told the BBC that he believed “140 or so” of his party colleagues had voted against the plans, along with “a small rump of Labour MPs” and “four Lib Dem MPs”.
He added: “Apparently there’s 132 Conservative MPs that voted in favour, so I think what we’re going to see is that more Conservative MPs voted against this legislation than for it.”
The bill would enable same-sex couples to get married in both civil and religious ceremonies, where a religious institution had formally consented, in England and Wales.
It would also allow couples who had previously entered into civil partnerships to convert their relationship into a marriage.
Just before the vote, Prime Minister David Cameron said: “Today is an important day. I am a strong believer in marriage. It helps people commit to each other and I think it is right that gay people should be able to get married too.
“This is, yes, about equality. But it is also about making our society stronger.
“I know there are strong views on both side of the argument – I accept that. But I think this is an important step forward for our country.”
Ahead of the vote, Culture Secretary and Minister for Equalities, Maria Miller, told MPs: “What marriage offers us all is a lifelong partner to share our journey; a loving stable relationship to strengthen us and a mutual support throughout our lives.”
She added: “I believe this is something that should be embraced by more couples. The depth of feeling, love and commitment is no different between same-sex couples than opposite-sex couples.”
Mrs Miller insisted religious freedom would be protected and that no faith organisations would be forced to marry gay couples.
She dismissed concerns from Tory opponents that the European Court of Human Rights could order British churches to marry gay couples.
“It is simply inconceivable that the court would require a faith group to conduct same-sex marriages in breach of its own doctrines” – not my words but the words of the eminent QCs, Lord Pannick, Baroness Kennedy and Lord Lester,” said Mrs Miller.
The Labour MP said in the Commons: “Call us hopeless romantics, call it the triumph of hope over experience, but most of us think it is wonderful when people love each other and want to make that long-term commitment.
“So why would we want to stop a loving couple getting married just because they are gay?”
The bill will now proceed to a parliamentary committee for further scrutiny.