"It has been the privilege of my life to serve you and this great country as prime minister, and I am confident that Britain is now stronger and fairer than it was two years ago," Starmer said in a farewell speech on Monday.
"I go with good grace. I go with a smile and I go proud of everything that we have achieved," he said to loud applause from the crowd that had gathered outside 10 Downing Street.
After Starmer formally resigned to the King at Buckingham Palace, Burnham, a former mayor of Greater Manchester, arrived to meet the monarch to be invited to form a government.
Burnham will be Britain's seventh prime minister in a decade, promising to "rewire" the nation to better focus on issues people care about, such as a cost-of-living crisis and poorly performing services.
Then the hard work begins.
Burnham, 56, faces a long list of problems, from Britain's underperforming utilities to anaemic economic growth, and must first unveil his top team of ministers - already the subject of much debate in the governing Labour Party.
Describing his election to become Labour leader as "the most significant change moment in our politics for 40 years", Burnham has promised to radically change Britain's political system to quickly raise living standards.
"The government I lead will confidently lay that path out starting next week," he said on Friday when he promised to offer Britain the hope and change the country "was crying out for".
"It will take us to a country where life is more affordable and all people and places are lifted from where they are now."
That message was made directly to Labour MPs who, after he returned to parliament last month, see him as one of the few politicians who can reduce the threat from veteran Brexit campaigner Nigel Farage's populist Reform UK party - something they doubted the unpopular Starmer could do.
Burnham's first hurdle will be the appointment of his cabinet team, particularly his choice of finance minister. Friction in this crucial partnership at the heart of government has led to the downfall of previous administrations.
An early frontrunner for the position, energy security and net zero minister Ed Miliband, has been on the receiving end of some hostile briefing and Interior Minister Shabana Mahmood now appears to be favourite for the job.
Burnham called on his party to ignore "speculation" on Friday and said he had not yet decided on his team.
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