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Thousands gathered in London's Trafalgar Square cheered as the announcement was made.

LONDON, England (CNN) -- London has defeated European rival Paris to host the 2012 Summer Games, bringing the Olympics back to Britain for the first time in more than half a century.

International Olympic Committee president Jacques Rogge made the announcement after IOC members voted 54-50 to eliminate the French capital in the fourth and final round of secret ballots Wednesday in Singapore.

"The International Olympic Committee has the honor of announcing that the Games of the 30th Olympiad in 2012 are awarded to the city of London," Rogge declared after opening a sealed envelope containing the result.

Thousands of people in London's Trafalgar Square cheered as they watched the announcement on giant TV screens. (Full story)

London has twice played host to the Olympics, in 1908 and 1948. It becomes the first city to host the Olympics three times.

British Prime Minister Tony Blair hailed the victory as "a momentous day for London."

In the French capital, groans of disappointment swept through a crowd of thousands gathered at Paris Town Hall.

It was the third defeat for Paris in 20 years, with bids for the 1992 and 2008 Games also failing.

Moscow, New York and Madrid were eliminated in the first three rounds of voting respectively. (More reaction)

The decision followed a final, furious lobbying effort by an elite "who's who" of politicians and athletes at the IOC's annual meeting.

Among the dignitaries who traveled to Singapore to lobby IOC members were Blair, French President Jacques Chirac, Queen Sofia of Spain and Russian Prime Minister Mikhail Fradkov.

The five cities bidding to host the 2012 Summer Games delivered their final presentations ahead of the vote.

London used royalty to get its message across, with Princess Anne kicking off the city's one-hour presentation with a message from Queen Elizabeth II.

"I've been impressed by the way everyone has united behind London's bid. As a country we share a passion for sport," the queen's message said, according to Reuters.

Blair, who held a string of meetings with IOC delegates before flying home to host the G8 summit in Gleneagles, Scotland this weekend, underlined London's message Wednesday with a pre-recorded video clip.

"Our vision is to see millions of young people participate in sport and improve their lives. London has the power to make this happen," Reuters quoted Blair as saying.

London also used the star power of David Beckham, one of the world's most famous soccer players, and Olympic gold medalist and bid chairman Sebastian Coe.

Chirac spoke passionately to the IOC, saying, "The heart of Paris and the heart of France are beating in unison in the hope of becoming Olympic host in 2012," The Associated Press reported.

"You can put your trust and faith in France, you can trust the French, you can trust us."

Paris also utilized the talents of actress Catherine Deneuve and French singer Johnny Halliday to highlight the wonders of Paris.

New York Mayor Michael Bloomberg, U.S. Senator Hillary Clinton and bid leader Dan Doctoroff used New York's readiness and its multicultural traditions to woo judges.

Bloomberg reminded the IOC of the city's recovery from the September 11, 2001, terrorist attacks.

"In our city's darkest hour, we asked ourselves, can we recover?" AP quoted him as saying. "New Yorkers stood up then and said, 'Yes, we can recover, we will rebuild and we must continue to welcome everyone. That spirit will be given to your Games."

U.S. President George W. Bush and former President Bill Clinton spoke in prerecorded video messages, AP said.

New York's delegation also included U.S. Olympic Committee Chairman Peter Ueberroth and a host of decorated Olympians, including Muhammad Ali, Nadia Comaneci, Ian Thorpe, Janet Evans and Jackie Joyner-Kersee.

Russian President Vladimir Putin's live video clip -- delivered in English -- urged the IOC to grasp a "unique and truly historic opportunity" by selecting Moscow, Reuters said.

"Moscow is a meeting place of cultures. Moscow is perfectly suited to host the Olympic and Paralympic Games," he said.

Russian swimming great Alexander Popov added: "If we can convince you to take this historic opportunity today, together we can change the world tomorrow."

Spanish Prime Minister Jose Luis Rodriguez Zapatero and Queen Sofie pressed Madrid's case.

"The whole Spanish royal family is convinced that Madrid fully meets the conditions to offer to the world the best Olympic Games," AP quoted the queen as saying.

Responding to questions from delegates, Madrid officials downplayed threats from the Basque extremist group ETA.

"Absolute security is assured," AP quoted Zapatero as saying.

"It's our main priority. Those who have tried to attack our candidacy will see that this is something that is doomed to disappear in Madrid and all of Spain."

Voting procedure

Voting has gone to four ballots in four of the last five votes to pick a host for the Summer Games. The only exception was in 2001, when Beijing was selected for the 2008 Olympics on just the second ballot.

London's bid was recently boosted by a survey of the world's top sports officials who favored its efforts over those of Paris.

The survey, by the Web site Sportcal.com, found there was little to choose between the bids technically.

"London received the strongest backing, partly on the basis that its presentations were thought to be the most professional of the five bidding cities," said the Web site.

The London-based site surveyed the secretaries general of National Olympic Committees (NOCs) and international sports federations by telephone and e-mail over the past two weeks.

The officials were asked which of the contenders they favored and why.

"Of almost 70 NOCs and federations surveyed, London's bid was the clear leader ... with 44 percent of respondents backing its bid, compared with 29 percent backing for Paris, 10 percent each for Madrid and New York and 7 percent for Moscow," Sportcal.com said in a statement.

"London received the backing of 31 percent of the federations, compared to Paris's 28 percent, New York's 19 percent and 11 percent backing for ... Madrid and Moscow."

As the clock counted down to the final vote, the lobby at the Raffles City Convention Center, the venue for the vote, was crammed with representatives of the bidding cities as they made their last-minute appeals.