Blair's exit was reportedly hastened by the two men falling out over Blair's failure to make good on a previous agreement to step down after two terms and hand leadership over to Brown.
The fallout led to an ugly last year in Blair's leadership marked by party infighting.
Tough tasks ahead
But Brown now has the chance to put all that aside. On Sunday, he will be named party leader at a specially convened conference in the northern city of Manchester, and three days later will assume the prime minister's office.
The 56-year-old Scot has a few years leading government before he faces what will likely be a tough battle in national elections in 2009 or 2010.
He has been tainted by his support for the unpopular war in Iraq, and accused by former aides of having an autocratic management style.
Brown has vowed to be his own man, but already has brushed aside suggestions he would loosen ties with George Bush, the US president - a point of disagreement among rank-and-file party members and large sections of the public who lambasted Blair as Bush's "poodle".
"Any foreign policy that I manage or have responsibility for has got be about our national interest, but it is in our national interest that the prime minister of the United Kingdom has a good relationship with the president of the United States," Brown said in a television interview.