London ? David Cameron, the youthful leader who modernized the party of right-wing icon Margaret Thatcher, became prime minister Tuesday after the resignation of Gordon Brown — capping a gripping election saga that returns the Tories to government after 13 years of Labour Party rule.

Following tradition, Queen Elizabeth II appointed Cameron at Buckingham Palace — a stately denouement to a behind-the-scenes dogfight between Cameron and Brown for the cooperation of Britain’s third-place party, after an election that left no party with a majority.

Within minutes, the 43-year-old Cameron was installed at No. 10 Downing Street, becoming the youngest prime minister in almost 200 years, since Lord Liverpool took office at age 42.

An announcement followed that Liberal Democrat leader Nick Clegg would become deputy prime minister — a rarely awarded and prestigious post — after days of hard bargaining with his former political rivals.

Cameron and Clegg agreed to form a coalition after Cameron’s Conservative Party won the most seats in Britain’s May 6 national election, but fell short of winning a majority of seats in Parliament.