House of Commons Speaker John Bercow told politicians that the royal assent had been given Wednesday - the day after the bill to legalise same-sex marriage in England and Wales cleared Parliament.
The queen's approval was a formality. It clears the way for the first gay marriages next summer.
The bill enables same-sex couples to get married in both civil and religious ceremonies in England and Wales. It also will allow couples who had previously entered into a civil partnership to convert their relationship to a marriage.
Britain’s same-sex marriage bill was
MPs decided not to oppose a number of minor amendments to the Marriage (Same Sex Couples) Bill proposed by the upper House of Lords.
Controversy over the issue among the Conservative Party has heaped pressure on Prime Minister and party leader David Cameron, who is already facing bitter opposition from many Tories over his leadership style and a promised referendum on Britain's EU membership.
Britain has seen none of the mass protests over gay marriage held across the channel in France, which last weekend became the 14th country in the world to legalise it.
Some 54% of Britons are in favour of allowing same-sex couples to marry, according to a YouGov poll for the Sunday Times.
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