As Big Ben struck 1630 IST, a two-minute silence was observed across Britain before the Queen laid the first wreath at the central London's Cenotaph war memorial.
The Queen joined more than 10,000 veterans and civilians, who then marched past the monument.
Services also took place at memorials across the UK, in Commonwealth countries and at military bases abroad.
The Last Post, the traditional trumpet call commemorating the war dead, was sounded following the silence, the monarch then laid her wreath at the foot of the monument, the focal point of the UK's Remembrance Sunday events since World War I.
Labour Party leader Ed Miliband, Lib Dem leader and Deputy Prime Minister Nick Clegg and Prime Minister David Cameron have laid wreaths.
The Remembrance service takes place every year on the nearest Sunday to the anniversary of the end of World War I on November 11, 1918. The day now also pays tribute to the dead in all conflicts, including World War II, Iraq and Afghanistan.