At a "special conference" on Friday, the former mayor of Greater Manchester will be elected after gaining overwhelming support from Labour MPs.
The event is little more than a formality before he replaces Keir Starmer as Britain's leader on Monday, when the party will be eager to find out his cabinet team and learn more about his approach to government.
Burnham, 56, will use his speech to press his message that his government will be "authentically Labour", overseeing economic renewal, more public control, re-industrialisation and putting power back in the hands of local communities.
He will promise to offer Britain "a new path to the one we've been on for the last 40 years" and his government will be "unashamedly Labour in our priorities and in the decisions we take, putting people and places at the heart of everything we do", according to extracts of his speech.
But there is still much to learn about how Burnham will govern.
He has given one speech since returning to parliament in June after winning a parliamentary seat in Makerfield, the start of a four-week process to install him as prime minister and remove Starmer, whose unpopularity across Britain turned his MPs against him.
In it, he sketched out some of his domestic agenda, saying he wanted to oversee the "biggest rebalancing of power" from London to Britain's regions - something he believes will reduce inequality and the anger felt by "left-behind communities" that have increasingly flocked to Reform.
That message of having a plan to thwart the rise of Reform 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.
