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.