After Blair's farewell in the House of Commons, Blair met with the queen at Buckingham Palace to offer his resignation, and then Brown spent nearly an hour with the monarch, The Times of London reported.
Brown was then taken to the prime minister's official residence and office at 10 Downing St., where he began organizing a Cabinet shuffle, with the first priority being his own replacement as finance minister.
The Telegraph said Alistair Darling was widely expected to become the new finance minister.
Brown, 56, has been trying to become leader of the Labor Party for the past 13 years. British media often reported that he chafed at his secondary role in government during Blair's 10 years and 57 days in power, the Times said.