At a "special conference" on Friday, Burnham, who earned the moniker "King of the North" for his determination as mayor of Greater Manchester to defend the region's interests, said he was ready for power and would work to offer hope to people in "forgotten places everywhere".
Warning that it was Labour's last chance to turn its fortunes around, the 56-year-old promised to spread power away from Westminster, the heart of British politics, to the nation's regions and preside over a "united" team to deliver the change the country was "crying out for".
"We are united and we put the power that comes from that unity at the service of people and places who have been waiting too long for politics to let them hope again," he told a room full of Labour MPs and party officials.
"And that's what we're going to do, everybody, we're going to give them hope back."
He also paid tribute to Keir Starmer, the man he will replace as prime minister on Monday, when the party will be eager to find out his cabinet team and learn more about his approach to government.
Despite repeating his offer to hand power to regions and to stop divisive briefings against Labour MPs who do not share his beliefs, there is still much to know about Burnham's policy priorities.
Burnham said he had not yet decided on his top team of ministers but would make sure it "reflects all parts of our party, all communities".
His victory speech, after a contest in which he was unopposed, did little to elaborate on the plans set out in the one speech he had given since returning to parliament in June after winning a seat in Makerfield, the start of a process to replace Starmer.
In it, he sketched out some of his domestic agenda, saying he wanted to oversee the "biggest rebalancing of power" to Britain's regions - something he believes will reduce inequality and the anger felt by neglected communities who have increasingly flocked to Reform and, in some cases, to the leftist Green Party.
On Friday, he said Labour could fight the threat from both of those parties not by trying to "out-Green the Greens or out-Reform Reform" but instead being "boldly, confidently, authentically us - Labour".
His message of having a plan to thwart the rise of Reform had won over Labour MPs, who feared they would lose their parliamentary seats to veteran Brexit campaigner Nigel Farage's populist party at the next national election, due by 2029.
Reform has topped opinion polls for months.
Some of that sheen has been tarnished in recent weeks by Farage's acceptance of funds from wealthy donors, perhaps giving Burnham an opening to revive Labour's fortunes.
Yet he does not have much time.
With a general election no more than three years away, Burnham will need to start implementing some of his pledges, many of which are based on long-term thinking, as quickly as possible.
He promised he would move quickly next week.
"The government I lead will confidently lay that path out, starting next week," he said.
"And that is why this change today is the most significant change moment in our politics for 40 years."
