John, 58, and Furnish, 43, were among hundreds of same-sex couples taking advantage of a new British law offering same-sex couples a legal status similar to marriage. The law took effect on Wednesday in England and Wales. Ceremonies were held earlier this week in Northern Ireland and Scotland.
Fans turned up before sunrise in the cobbled streets around Windsor's town hall, the Guildhall, where Prince Charles and Camilla Parker Bowles wed in April. Cameras flickered as the couple — John wearing purple spectacles and a black suit — walked out arm-in-arm, waving to the crowd.
The couple drove off in a black Rolls Royce for a lunch followed by a glitzy reception to be attended by more than 700 guests.
"I think it's amazing — it's brilliant," said Tim Alcock, 43, one of dozens of onlookers.
Prime Minister Tony Blair, speaking to reporters at a news conference, wished the couple well and congratulated them for exercising their newfound legal right. Gay rights activists saw the union as milestone in gay rights movement.
Peter Tatchell, spokesman for the gay and lesbian human rights group OutRage! said the wedding "would raise the profile of gay love and commitment."
"Their same-sex civil partnership ceremony will be reported all over the world including in countries where news about gay issues is normally never reported," he said. "This will give hope to millions of isolated, vulnerable, lesbian and gay people especially those living in repressive and homophobic countries."
The new law — passed last year despite some opposition from Parliament's unelected House of Lords — allows civil ceremonies that will give same-sex couples the same social security, tax, pension and inheritance rights as married couples.
Furnish, a Canadian-born filmmaker, and John have been together for 12 years. Both acknowledged that their ceremony might have broader ramifications.
"As far as I'm concerned I've always considered myself committed to Elton and he's the person that I want to spend the rest of my life with. So in that sense I don't feel like the dynamic of our relationship is going to change," Furnish told Attitude magazine. "But from a social standpoint, I think it's hugely significant. It is a major, major change. It is one of the defining issues of our times."
After the ceremony the couple headed for a lunch with their family to be followed by a reception — costing an estimated $1.75 million — where pink champagne and lamb would be served to hundreds of celebrity guests inside two giant white tents that have been erected on the grounds of the pop star's Windsor mansion.
Their morning ceremony, in contrast, was low-key with only John's mother and stepfather and Furnish's parents reportedly in attendance.
Guests at the couple's bachelor night on Monday included heavy metal rocker turned reality TV star Ozzy Osbourne and his wife Sharon, model and actress Liz Hurley and musicians Bryan Adams, Gary Barlow and Kid Rock.
John, who was married once before to studio engineer Renate Blauel, is known for such songs as "Crocodile Rock" and "Rocket Man." He was also a very close friend of Princess Diana, who died in a car crash in Paris in 1997, and was knighted in 1998 — an honor he described as the pinnacle of his decades-long career.
"It's a long time coming really," said Suzi Uprichard, 33, of Maidenhead, who was in the crowd in Windsor. She said she was excited to be part of what she described as a historic day for same-sex couples.
Other couples tying the knot Wednesday included actor Sir Antony Sher, 56, and his partner Greg Doran, 47, who wed at Islington Town Hall in north London.
Three couples signed their documents moments after the register office opened at 8 a.m. in Brighton, the south coast city known as Britain's gay capital.
"I'm really excited! I'm very happy to be one of the first," said Gino Meriano, who was with his partner Mike Ullett.
The Netherlands, Canada, Belgium and Spain have legalized same-sex marriage, while Germany, France and Switzerland have laws similar to Britain's. In the United States, only Massachusetts allows gay marriage, while Vermont and Connecticut permit civil unions.