In a spectacular display of precision marching and horsemanship choreographed to military band music, about 1,220 soldiers in ceremonial red dress and huge black bearskin caps saluted the monarch in the Trooping the Color ceremony at the Horseguards Parade ground near Buckingham Palace.
The "color" being paraded on London's Horse Guards this year is the flag of the 1st Battalion Irish Guards, and some of the soldiers involved were Iraq war veterans.
The queen turned 79 on April 21, but public celebrations of the British monarch's birthday are always held on a Saturday in June, when the chances of fine weather are good.
Thousands of people filled sidewalks around palace on a partly cloudy day, hoping to catch a glimpse of the queen.
"I've got goose bumps. It's wonderful. I've got to see the queen," said Beryl Sixsmith, 64. She had come to London from her home near Manchester, a city in northern England.
The queen and her husband, Prince Philip, who celebrated his 84th birthday Friday, rode in an open carriage from Buckingham Palace along the wide, tree-lined Mall from the palace to the parade ground near Admiralty Arch.
Prince William, 22, elder son of Prince Charles and the late Princess Diana, rode in a separate a carriage with his stepmother, the Duchess of Cornwall. The duchess, the former Camilla Parker Bowles, married Prince Charles on April 9.
After the hour-long ceremony, the queen and her family gathered on the palace balcony to watch Royal Air Force jets fly overhead in her honor.
"It makes me proud to be British when I see the soldiers marching down the Mall in perfect formation," said Michael Woolstenholmes, 52, a retired teacher in London.
Earlier Saturday, the queen released her annual list of birthday honors to many Britons, including veteran rockers Brian May, Jimmy Page, John Mayall and Midge Ure.