Prime Minister David Cameron has hailed the first gay weddings in England and Wales as sending a "powerful message" about equality in the UK.
The law changed at midnight, with a number of gay couples vying to claim the title of being among the first to be married as ceremonies took place across England and Wales.
Despite facing opposition from some in the Conservative Party about his backing for the change, Mr Cameron said the reform was necessary because "when people's love is divided by law, it is that law that needs to change".
Writing in Pink News, he said: "This weekend is an important moment for our country" because "we will at last have equal marriage in our country".
"The introduction of same-sex civil marriage says something about the sort of country we are," he added.
"It says we are a country that will continue to honour its proud traditions of respect, tolerance and equal worth. It also sends a powerful message to young people growing up who are uncertain about their sexuality.
"It clearly says 'you are equal' whether straight or gay. That is so important in trying to create an environment where people are no longer bullied because of their sexuality - and where they can realise their potential, whether as a great mathematician like Alan Turing, a star of stage and screen like Sir Ian McKellen or a wonderful journalist and presenter like Clare Balding."
Among the first couples set to take advantage of the legalisation were actor Andrew Wale, 49, and guesthouse owner Neil Allard, 48, who wed at the Royal Pavilion in Brighton just after midnight.
Following the ceremony in which the couple wore matching suits, Mr Wale told Sky News: "It’s a wonderful feeling, it was much more emotional than I thought it was going to be and I’m just kind of happy and buzzing."
Mr Allard added: "It’s exciting, it’s a new step forward and it’s all about love."
Being Transgender or Gay is not a choice, being Transphobic or Homophobic is, so don't be a Twonk