By Zachary Roth

It’s official!

A smiling Prince William and Kate Middleton were declared man and wife at London’s Westminster Abbey, in front of a congregation of around 1,900 and a worldwide television audience estimated at as many as 2 billion.

Wearing an ivory and white satin dress designed by Sarah Burton–a closely guarded secret until minutes before the service began–Kate accepted a wedding ring of Welsh gold, given to William by the Queen soon after the couple were engaged. The bride also wore a diamond-studded halo tiara loaned by the Queen, with her gently curled hair down at the back.

In a marriage ceremony led by Archbishop of Canterbury Rowan Williams, Kate promised William that she would “love him, comfort him, honor him, and keep him,” and he offered the same pledge. Like William’s mother Princess Diana at her own 1981 wedding to Prince Charles, Kate struck a modern note by omitting the traditional vow to “obey” her husband.

[ Photos: Check out a gallery of Kate’s wedding dress ]

William, who chose not to wear a ring, donned a bright red tunic, with a crimson and gold sash and gold sword slings, from the Irish National Guards, a British Army regiment of which he is an honorary colonel. The choice was made in part to honor three members of the Guards who were killed in action in Afghanistan.

The bride’s ring was created by Wartski, a Palace spokesperson said, a family jeweler that also created the wedding bands for Prince Charles’s 2005 marriage to Camilla Parker Bowles, now the Duchess of Cornwall.

Kate, 29, the daughter of creators of a successful party-planning business, becomes the first commoner in line to be queen in modern times. She’ll now be known officially as Her Royal Highness the Duchess of Cambridge, Buckingham Palace said in a statement this morning–though the public will know her as Princess Catherine. William becomes the Duke of Cambridge.

The bride’s three-and-half minute procession through the abbey was accompanied by a choir singing the soaring English choral “I Was Glad,” composed in 1902 by Sir Charles Hubert Hastings Parry. In a tribute to Princess Diana, the congregation began the service by singing “Guide Me O Thou Great Redeemer,” a Welsh hymn sung at her 1997 funeral. It also sang “Jerusalem,” the popular English hymn based on a poem by William Blake.

[ Related: The best hats from the royal wedding ]

Prince Charles and the Duchess of Cornwall, along with Kate’s parents, Michael and Carole Middleton, served as witnesses and signed the marriage registers. The bride’s mother wore a gray-blue dress designed by Catherine Walker, a fashion designer whose work was championed by Princess Diana. The Duchess of Cornwall opted for a champagne silk dress designed by Anna Valentine, and a Philip Treacey hat.

The hour-long service was conducted by the Very Reverend Dr. John Hall, the dean of Westminster. It also included an address from the Right Reverend Richard Chartres, the bishop of London and a friend of the royal family.

William, 28, spent a low-key last bachelor evening with his father at St. James’s Palace, then traveled this morning to the abbey in a uniquely designed Bentley, with his best man, Prince Harry–both brothers smiling and waving through the window to the crowds. Before the service, they greeted members of the congregation, including Earl Spencer, Princess Diana’s brother.

Kate, meanwhile, stayed the night with her family–including her maid of honor, younger sister Philippa–at London’s Goring Hotel, and came to the abbey alongside her father in a Rolls-Royce Phantom VI owned by the queen.

After the service, the newlyweds are set to ride to Buckingham Palace in a horse-drawn open-top carriage–originally built in 1902 for William’s great-great-great grandfather, King Edward VII. They’ll pass Parliament Square, Whitehall, and the Mall along a processional route, lined since yesterday–despite the chilly and overcast weather–with crowds cheering and waving the Union Jack, having heard the service over loudspeakers.

At the palace, the Queen will host a lunchtime reception for a select 650 members of the congregation, during which William and Kate will appear on the balcony–weather permitting–for what’s expected to be their first public kiss as newlyweds. Later, they’ll head to a roughly 300-person dinner and dance party given by Prince Charles, also at Buckingham Palace. The Queen, who wore an Angela Kelly primrose dress and matching coat, will skip that event, the Palace has said, to allow the younger crowd to properly let their hair down.

Elsewhere, millions of Britons took advantage of the national holiday–declared months ago by Prime Minister David Cameron–by gathering in pubs, private homes, and public viewing areas to celebrate the event, which for months has dominated the country’s news coverage. Estimates for the hit to Britain’s economy, thanks to the day off work, have ranged from $10 billion to $50 billion.

[ Photos: See images of the royal wedding party]

Cameron, who famously camped out on the Mall for Charles and Diana’s wedding, called the day “a chance to celebrate.”

“We’re quite a reserved lot, the British,” the prime minister told the BBC this morning. “But then when we go for it, we really go for it.”

The wedding congregation mixed personal friends of the bride and groom, royalty from around the world, dignitaries from numerous former British colonies, foreign officials and diplomats, and celebrities including Elton John and David and Victoria Beckham.

Representatives of all governments with whom Britain has normal diplomatic relations had originally received invitations. But the Syrian ambassador was informed yesterday that he was no longer welcome, amid a violent ongoing crackdown against pro-democracy protesters carried out by the regime of President Bashar Assad. The presence of the Bahraini ambassador, who previously ran a government agency accused of using electric shocks and beatings, has also provoked controversy.

[ Related: All of the details on Kate’s dress]

Adding to the rancor over the guest list, two former Labour Party prime ministers, Tony Blair and Gordon Brown, were not invited, even as two former Conservative PMs, Baroness Thatcher and Sir John Major, were included–an arrangement that was criticized by several Labour members of parliament (Thatcher was too unwell to attend). St. James’s Palace said that Thatcher and Major received invitations because they’re both Knights of the Garter, unlike Blair and Brown. Major also was appointed a guardian to William and Harry after Diana’s death.

The wedding caps a nearly decade-long relationship for William and Kate, who met in 2001 as students at the University of St Andrew’s in Scotland, and began dating a year or so later. Aside from a brief reported split in 2007, they appear to have been an item ever since. William proposed during a vacation in Africa last October.

The pair’s lengthy buildup contrasts with that of Prince Charles and Princess Diana, who were estimated to have spent just 21 hours together before marrying. That famously troubled union ended in divorce in 1996, after a long estrangement. Diana died in a car accident in Paris the following year.

The wedding comes at a pivotal time for the House of Windsor. Though she appears to remain in good health, the 85-year-old Queen reportedly has begun planning for her funeral. Charles, the heir to the throne, is seen by much of the public as stiff and out of touch, prompting concern that his accession could undermine the monarchy’s standing with the public. Polls indicate that upon the Queen’s death, most Britons would like to see the throne skip straight to William, though that currently appears unlikely.

In addition to being given the titles of Duke and Duchess of Cambridge, the couple will also become the Earl and Countess of Strathearn, as well as Baron and Baroness Carrickfergus.