At the stroke of midnight on Friday night, same-sex marriage finally became official and legal in England and Wales. Scotland will follow soon, with the first ceremonies expected in October. Northern Ireland has not yet followed suit.
Dozens of eager couples finally tied the knot in midnight ceremonies south of the Border.
England is the 16th country worldwide to have legalised gay marriage - the Netherlands was the first, more than a decade ago.
Among the first to celebrate the UK's change was radio presenter Sandi Toksvig and her partner, Debbie, at the Royal Festival Hall in London's South Bank.
The couple, who had entered into a civil partnership seven years ago, described the day as "an astonishing moment in history".
Toksvig added: "There was many a time I thought this day would never come. We're still crazy about each other. I can't believe my luck - look how gorgeous she is. I want a piece of paper to say she won't ever leave me."
Across the city, at Islington Town Hall, the first Scot to wed was writer Peter McGraith from Lanarkshire. He and his partner, David Cabreza, have been together for 17 years.
The couple dedicated their big day to all those who continue their struggle for equal rights.
McGraith said: "The battle for equality is an ongoing struggle, and my part in that fight will not stop on my wedding day.
"I feel privileged to be married on this day, while at the same time being able send a message of solidarity and hope to all those who are denied this right."
Activist Peter Tatchell - a long time advocate of same-sex marriage - took on the role of celebrant and chief witness at the McGraith-Cabreza wedding.
Tatchell said: "Same-sex marriage is an unstoppable global trend because love and commitment are universal human traits, regardless of sexual orientation or nationality. No ignorance or prejudice can hold back the triumph of love. I rejoice that the ban has finally been lifted and I look forward to the advent of same-sex marriage in Scotland."
Despite Holyrood acting before Westminster in legislating for same-sex marriage, MPs were able to craft and refine their Bill before MSPs. The Scottish Parliament first started its deliberations in September 2011.
Alex Neil, Cabinet Secretary for Health and Wellbeing, said: "We have been thorough in making sure we get this legislation absolutely right to ensure everyone had a chance to have their say.
"Now our Bill has received Royal Assent, we are continuing to move forward to implement the statutory changes necessary to ensure that same-sex couples have the same rights and privileges as every other married couple.
"Key to achieving this is our work with the UK government to amend the Equality Act, as power in this area is currently reserved to Westminster."
Tim Hopkins, director of gay rights group Equality Network, said: "Westminster rushed through the first and second stages of the Bill, whereas Holyrood has been decidedly more careful in its approach. As a result, the Bill in Scotland is perhaps a little bit stronger here than it is down south, with a more sensitive approach."
However, one of Scotland's same-sex "power couples", the novelists Louise Welsh and Zoë Strachan, feel Scotland should have moved to keep pace with England and Wales.
Strachan said: "I'm disappointed that the equal marriage legislation has taken so long in Scotland. I remember responding to the first consultation over two years ago and I'm not sure why Scotland has been dragging its feet over the law.
"It doesn't make sense to argue that England simply rushed their Bill. The law is not about gay rights, it is about equality of human rights and addressing the current imbalance.
"We would never hear about a government 'rushing' any other equal rights legislation, as we'd all agree that it is something that should have been in place to begin with."
Welsh added: "Scotland has a record of lagging behind England on legislation granting equality for LGBT people - homosexuality was legalised for men in 1967 in England, while it was 1980 in Scotland.
"I feel very happy for those in England who are able to celebrate equal marriage today, but must admit to feeling a pang that we do not yet have the same rights in Scotland."
It is estimated that around two-thirds of people in the UK support marriage equality for same-sex couples.
But some religious groups still maintain their opposition, and claim they could face discrimination for their beliefs.
The Reverend David Robertson, a minister in the Free Church of Scotland, said: "There is a public conception that those who do not favour same-sex marriage are therefore homophobic.
"I believe homophobia is wrong, but I hold the traditional view that marriage should be a union between a man and woman.
"This definition means I would refuse officially to recognise same-sex marriage but I feel these beliefs will leave me, and those who share this view, open to discrimination. People will brand us as idiots, small-minded and say we sit on the fringes of society.
"So I wouldn't say this redefinition of marriage should be celebrated, as so many risk marginalisation as a result."
And SNP MSP John Mason claimed a person's opposition to same-sex marriage could leave them open to prosecution.
He said: "I'm not convinced there are adequate legal safeguards in place to protect those who express their opposition to same-sex marriage. It remains to be seen whether court proceedings would result in Scotland, but we do feel that courts would be inclined to support such actions."