The 89-year-old monarch, senior royals and politicians including Prime Minister David Cameron laid wreaths at the Cenotaph national war memorial in London, as thousands of military veterans looked on.
King Willem-Alexander of the Netherlands laid a wreath to mark the 70th anniversary of the liberation of the Netherlands after the end of World War II.
Opposition Labour leader Jeremy Corbyn also laid a floral tribute. The long-time pacifist wore a poppy, and sang the national anthem, having previously been criticised for remaining silent during its playing.
Thousands of veterans earlier marched past the Cenotaph, Britain's primary war memorial.
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Later today, a projection of giant falling poppies -- the flower that has symbolised the nation's war dead since World War I -- will be projected onto the Houses od Parliament.
Remembrance Sunday is the Sunday nearest to Armistice Day on November 11, the anniversary of the 1918 signing of the peace that ended fighting in World War I.
It is thought there has been only one year -- 1968 -- without a British military fatality on active service since the end of World War II in 1945.