Peers have voted by more than two to one to back government plans for same-sex marriages in England and Wales.But it rejected an amendment aimed at wrecking the bill by 242 votes, moving it a step closer to becoming law.
The government wants same-sex marriages - which were approved by MPs last month - to be available by next summer.
The bill would allow couples, who can currently form civil partnerships, to marry.
If it passes into law, religious organisations would have to "opt in" if they wished to offer gay weddings, except the Church of England and Church in Wales, which would be banned in law from doing so.
Leaders' backing
Peers were allowed a free vote on the amendment, tabled by crossbench peer Lord Dear, which would effectively have wrecked the government's plans. It was defeated by 390 votes to 148.
Shortly afterwards, the bill was given a second reading without a vote taking place and will now go forward to more detailed scrutiny by peers.
The result was greeted with cheers from supporters of same-sex marriage gathered outside Parliament.
During the debate, Lord Dear insisted the change would "completely alter the concept of marriage as we know it".
The bill was "ill thought through", had no democratic legitimacy and was "fatally flawed", he said.
But equalities minister Baroness Stowell of Beeston called the legislation a "force for good" which would strengthen marriage.
She said it protected both religious freedom and freedom of speech.
The plans passed through the Commons last month with a 205 majority.
They are backed by Prime Minister David Cameron, his Liberal Democrat deputy Nick Clegg and Labour leader Ed Miliband.
But religious bodies, including the Church of England, and many Conservative activists have raised concerns.
The Archbishop of Canterbury, Justin Welby, was among those who spoke against the proposal in the Lords.
France recently held its first same-sex marriage while the Scottish government has confirmed it will introduce a bill shortly.