He came to power in 1997, and proved to be very valuable to England when she lost one of her biggest stars - Diana, Princess of Wales. Calling her "the people's princess," he accurately judged the mood of the nation when the House of Windsor did not. Ten years later, he's stepping down after taking some hard knocks for his stance on Iraq.
He will stay on in Downing Street until the Labour Party elects a new leader - widely expected to be Gordon Brown.
Mr Brown, who is expected to launch his leadership campaign on Friday, paid tribute to Mr Blair, saying: "I think I spoke for millions when I said at Cabinet today that Tony Blair's achievements are unique, unprecedented and enduring."
He said people would remember "how he led the country after 7 July, how he responded for the world after 11 September in America, how he responded to the tragic death of Princess Diana".
More: The Blair era ends