The MP for Makerfield cemented his status as the sole leadership candidate after being backed by 379 Labour MPs, as well as all 11 trade unions affiliated to the party, earlier this week.
Having run twice before to become Labour leader, his successful bid this time round marks a rapid rise to power following the former Greater Manchester mayor’s by-election win in Makerfield last month.
In his first speech as Labour leader at the TUC headquarters in central London, Burnham rejected the “neoliberal” policies of the past 40 years, including when he was in government, and vowed to reindustrialise the country.
Promising to lead a government that is “distinctively Labour,” he said: “Britain took a series of wrong turns in the 1980s – political power was centralised and economic power was privatised.
“The country surrendered control of the essentials.”
And in a message to Labour MPs, he said he would work relentlessly to build a culture of “one Labour team”.
“We won’t beat Britain’s new right if we are consumed by infighting and pulling in different directions,” he said.
He added that his approach to governing would be characterised by “problem-solving rather than point-scoring”.
He said he had made no decisions about who would be in his cabinet but that it would reflect “all parts of our party” and “all communities”.
There has been widespread speculation about who will be taking the top jobs, with Ed Miliband and Shabana Mahmood thought to be in the running to replace Rachel Reeves as chancellor.
Since announcing his intention to stand to replace Sir Keir, Burnham has given little detail about his policy plans.
His speech on Friday was light on specifics, which are expected to come as he moves into Downing Street next week.
Reflecting on his time in political life, he said: “I haven’t got everything right and I’m sorry where I’ve fallen short. But I have always given it my all and I always will.”
He added that he knows what he believes and what he wants to do in government, telling the audience: “I have a plan.”
Linda Hobson, from Unison, one of the unions linked to Labour, said Burnham “must get this right and bring back the hope he promises”.
“The union looks forward to working with him to bring about the transformation so desperately needed for the UK and the emphasis on Labour values,” she said.
Having run twice before to become Labour leader, Burnham’s successful bid this time round marks a rapid rise to power following the former Greater Manchester mayor’s by-election win in Makerfield last month.
Labour has trailed Reform UK in opinion polls for almost 18 months and supporters will be hoping Burnham’s arrival as prime minister will reverse their fortunes.
Sir Keir resigned as Labour leader last month, saying he accepted he was not best placed to lead his party into the next general election.
Heavy Labour losses in May’s local elections followed by Burnham’s by-election victory in Makerfield had left Sir Keir facing widespread calls from his own MPs for him to stand aside and allow Burnham to replace him.
Burnham paid tribute to Sir Keir, celebrating his record in government including improving rights for workers and renters, seeing NHS waiting lists fall and bringing rail back under public control.
