Homosexual Britons living in more than 20 foreign countries where same-sex marriage is not allowed can now marry their partners at British consulates.
Russia, China, Kosovo and Vietnam are among the countries included in new legislation which came into force on Tuesday.
Homosexual lobby group Stonewall welcomed the move, saying they hoped all countries would one day introduce same-sex marriage.
Chris Bryant, a former Foreign Office Minister, said: “Part of the Foreign Office’s job is to export British values abroad.”
The Government says authorities in the countries have given permission for the British consulates to carry out the same-sex marriages.
The Consular Marriage and Marriages under Foreign Law Order 2014 means a total of 23 British consulates will be allowed to have the ceremonies.
The list includes Australia, Azerbaijan, Bolivia, Cambodia, Chile, China, Colombia, Costa Rica, Dominican Republic, Estonia, Hungary, Japan, Kosovo, Latvia, Mongolia, Montenegro, Nicaragua, Peru, Philippines, Russia, San Marino, Serbia and Vietnam.
The Marriage (Same Sex Couples) Act, covering England and Wales, received Royal Assent last year – despite widespread opposition.
In Scotland a Bill to redefine marriage was passed by MSPs earlier this year, but the Northern Ireland Assembly has three times rejected proposals to make a similar move.
In July David Cameron said he wanted to export same-sex marriage around the world, as he held a Downing Street party for gay activists.
He claimed the legislation in England and Wales was passed in “good time”, adding: “Many other countries are going to want to copy this”.
The Prime Minister added that the team that worked on the Bill “can be part of this global race and take it around the world”.
Mr Cameron was criticised for the stance by columnist Richard Littlejohn, who commented: “What does he hope to achieve by embarking on a mission to proselytise same-sex marriage around the world, other than to bask in the admiration of the gay lobby?
“It will only serve to reopen old wounds and alienate still further many of his own supporters, already heading to UKIP in droves.”