The first same-sex weddings in England and Wales will be able to take place from 29 March 2014, Equalities Minister Maria Miller says.
Initially it was thought the first marriages would not take place until next summer.
Couples wishing to be among the first to marry will need to give formal notice of their intention by 13 March.
It comes after the government's controversial legislation on the issue received Royal Assent in July.
The Conservative, Labour and Liberal Democrat leaderships all backed the proposals.
MPs approved the principle of same-sex marriage despite opposition from many Conservatives, which caused tensions in the party. Most Lib Dem and Labour MPs supported the move.
The Church of England, the Church in Wales and other faith groups stated their opposition.
Following the passing of the Marriage (Same-Sex Couples) Act, the government has been able to put in place the necessary arrangements much faster than previously thought.
'Open to everyone'
Ms Miller said: "Marriage is one of our most important institutions, and from 29 March 2014 it will be open to everyone, irrespective of whether they fall in love with someone of the same sex or opposite sex."
She said it was "just another step in the evolution of marriage".
And she said she was "working hard" to ensure that couples who wanted to convert civil partnerships into marriages - and married people wanting to change their legal gender while remaining married - would be able to do so before the end of next year.
From June, people will also be able to take part in same-sex weddings in some British consulates and armed forces bases overseas or in military chapels.
Ben Summerskill, chief executive of gay rights campaign group Stonewall, said he was "delighted" at the announcement.
He said: "This historic step will mean that, for the first time, every gay person in England and Wales will finally enjoy exactly the same rights as their heterosexual friends and family."
Lib Dem leader Nick Clegg said on Twitter: "Great news that same sex weddings will happen from 29th March 2014 #savethedate."
Labour's shadow minister for women and equalities, Gloria De Piero, said it was "fantastic news for so many couples who have been waiting to set a date for their wedding".
Under the terms of the bill, religious organisations will have to "opt in" to offering weddings, with the Church of England and Church in Wales being prevented in law from doing so.
A report commissioned by the Church of England published last month recommended that members of the clergy should be allowed to offer blessings to same-sex couples.
The Church said the report was for discussion and was "not a new policy statement". The report did not propose offering "formal" ceremonies.
The Roman Catholic Church in England and Wales, the Muslim Council of Great Britain and the Network of Sikh Organisations have opposed plans to allow gay marriage.
Among Jews, the Liberal and Reform synagogues support gay marriage while the United Synagogue opposes it.
Quakers have campaigned in favour of same-sex marriage and will allow ceremonies to take place on their premises.
The Scottish Parliament has approved in principle legislation to introduce same-sex marriage, which is opposed by the Church of Scotland and Catholic Church.
The Northern Ireland Assembly is not currently considering any legislation to allow same-sex marriage.