Mr Brown returned to Downing Street from Buckingham Palace as Britain's new Prime Minister and declared: "I will try my utmost." Standing outside 10, Downing Street with his wife Sarah he also pledged to be "strong in purpose, steadfast in will and resolute in action".
Mr Brown told reporters: "I have just accepted the invitation of Her Majesty the Queen to form a Government.
"This will be a new Government with new priorities and I have been privileged to have been granted the great opportunity to serve my country." He promised to be at all times "strong and steadfast" and to govern beyond narrow political interests.
Tony Blair's resignation after 10 years finally cleared the way for Mr Brown to fulfil his ambition to run the country.
Mr Blair, after his meeting with the Queen took the train to his constituency of Sedgefield. He is expected to step down as the MP from his constituency after 24 years, to take up the job of envoy of the Quartet of West Asia.