Brown secured nominations from 313 of the House of Commons' 354 fellow Labour MPs, becoming the de facto party leader before his formal confirmation June 24.
His only challenger, John McDonnell, withdrew from the race Wednesday over a lack of support to qualify.
Brown said that upon assuming the premiership next month, he would try to maintain Britain's steady economic growth, widely seen as the result of his own efforts as the Treasury chief, and would work to improve public health, education and welfare, as well as to restore trust in British democracy.
He announced no change on Britain's military commitment in Iraq, despite promising earlier this month to learn from the mistakes of the Iraq war, which are partly to blame for Labour's dwindling popularity.
"I do believe we are in a new stage now where people of this country recognize our obligations to a newly elected Iraqi government."
Nor did the prime-minister-in-waiting signal any shift in London's relationship with Washington, despite wide discontent among the British public with the outgoing premier's staunch pro-Americanism.
"The relationship between a British prime minister and an American president must and ought to be a very strong one, and I look forward to building that relationship with the president of the United States," Brown said.
Prime Minister Tony Blair, who announced his impending resignation May 10 after a decade in office, is to hand over the Downing Street keys June 27. But many urge him to transfer earlier, with the election of his successor already a done deal.
Conservative Party leader David Cameron has complained about a current power vacuum, with Blair away on a long farewell tour overseas.
News Statesman Editor John Kampfner has described the situation as "a vanity policy," but said that on the up side, Brown would have plenty of time to consider candidates for his Cabinet before the formal transition of power June 27.
Six candidates will meanwhile be competing for the position of deputy Labor leader and prime minister, to replace John Prescott.
Education Minister Alan Johnson is leading the race with 73 votes in his favor, followed by Constitutional Affairs Secretary Harriet Harman and the Secretary for Wales and Northern Ireland, Peter Hain.
