The vote in the House of Commons -- 400 to 175 in support of the proposed legislation -- will be followed by more detailed parliamentary debates. The proposals also require the approval of the House of Lords before they become law.
The process could take months, but if approved, the bill is expected to take effect in 2015 and enable same-sex couples to get married in both civil and religious ceremonies, provided the religious institution consents. The bill also lets couples who had previously entered into civil partnerships convert their relationship into a marriage.
"Tonight's vote shows Parliament is very strongly in favor of equal marriage," Deputy Prime Minister Nick Clegg said. "I genuinely believe that we will look back on today as a landmark for equality in Britain."
The lopsided vote was a qualified victory for Cameron, with around half of his party's lawmakers rejecting the proposals or abstaining. Nonetheless, strong support from the left-leaning Labour Party and Liberal Democrats party ensured the Commons approval.
After the ballots were counted, Cameron acknowledged that "strong views exist on both sides," but said the result was a "step forward for our country."
Officials have stressed that all religious organizations can decide for themselves if they want to "opt in" to holding gay weddings. However, the Church of England, the country's official faith, is barred from performing such ceremonies.
That provision aims to ensure that the Church, which opposes gay marriage, is protected from legal claims that as the official state religion it must marry anyone who requests it.
Currently, same-sex couples only have the option of a civil partnership, which offers the same legal rights and protections on issues such as inheritance, pensions, and child maintenance.
Supporters say that gay relationships should be treated exactly the same way as heterosexual ones, but critics worry that the proposals would change long-standing views about the meaning of marriage. Some Conservatives also fear the proposals would cost the party a significant number of votes in the next general election.
"Marriage is the union between a man and a woman, has been historically, remains so. It is Alice in Wonderland territory, Orwellian almost, for any government of any political persuasion to seek to come along and try to re-write the lexicon," Conservative lawmaker Roger Gale said.
The bill's provisions apply only to England and Wales -- there are no plans for similar legislation in Northern Ireland. Scotland is considering introducing a similar bill.
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