Acting Labour leader Harriet Harman said the Queen is "admired by billions of people all around the world" in a tribute to her in the House of Commons.
Ms Harman praised Her Majesty's "tireless" commitment and dedication to the service of her country.
She also joked that the Queen had "gone from sending telegrams to sending tweets".
"We send her out warmest congratulations, our appreciation and above all our thanks," said Ms Harman.
Could overseeing the development of the Commonwealth be the Queen's greatest international success?
As Queen Elizabeth II becomes the country's longest reigning monarch, ITV News looks back at her remarkable rule.
Fashion and portrait photographer David Bailey said the Queen has the most recognisable face in the world and a "twinkle in her eye".