Andy Burnham, the man about to become Britain’s next prime minister, looked exhausted and on the edge of fury.

It was October 2020, the depths of the Covid-19 pandemic. As mayor of Greater Manchester, he had just learned from an aide that the Conservative government in London, some 200 miles south, had imposed fresh lockdown restrictions on his area, while refusing his demand for $87 million to protect low-income workers and struggling businesses.

“This is no way to run the country in a national crisis,” he fumed in front of a Manchester concert hall. “They should not be doing this. Grinding people down. Trying to accept the least they can get away with.”

“It is frankly disgraceful,” he said.

The video clip went viral, earned Mr. Burnham the nickname “King of the North” and was arguably the moment that set him hurtling toward No. 10 Downing Street.

On Friday, he will become the leader of the Labour Party and on Monday, King Charles III will formally ask him to become the country’s 59th prime minister.

Mr. Burnham’s brand has always been that of the plain-spoken, stand-up-for-the-little-guy politician. Despite his highbrow English degree from Cambridge University, his regional accent communicated his ordinary upbringing in northwest England. Born in 1970, Andrew Murray Burnham grew up in a close-knit Roman Catholic family in the village of Culcheth, between two postindustrial cities in decline for decades: Liverpool, where he was born, and Manchester.

“Our lifestyle was modest, and we never had a family holiday abroad,” he wrote in “Head North,” his 2025 memoir. “But we didn’t want for anything.”

As an ambitious young member of Parliament, he quickly rose through the ranks even as he lost two bids to become Labour Party leader. He was a junior minister under Tony Blair and a member of Prime Minister Gordon Brown’s cabinet before growing disillusioned with London and returning home to run one of Britain’s largest cities.

Now, he will replace Keir Starmer, one of the most unpopular British leaders in modern history. It is not clear how Mr. Burnham intends to overcome the challenges that doomed his predecessor: high government debt, slow economic growth, aging infrastructure and political division.

“Andy Burnham is fundamentally an instinctive politician,” said Joshi Herrmann, a journalist and the founder of The Manchester Mill, who has covered Mr. Burnham for years. “That’s a valuable skill set,” he said. “But it’s naïve to think that a better communicator is going to get around these fundamental problems of British life.”

‘Not for people like me’

Mr. Burnham was 17 when the rejection came.

By his own admission, the interview in the wood-paneled room at St. Catharine’s College, Cambridge University, had gone poorly. He had fumbled a question about The Canterbury Tales and accepted that the “completely alien world” of one of Britain’s elite universities was out of reach.

Instead, on his 18th birthday in 1988, he was back at Cambridge for another interview, this time with Fitzwilliam College, which offered him a place.

It was Stephen Harrington, his English teacher at St. Aelred’s Catholic High School, who urged a reluctant Mr. Burnham to set his sights on Cambridge.

“It was very much ‘Oh, no, no. That’s not for people like me,’” Mr. Harrington recounted to the BBC.

If he was uncertain that he belonged there, Mr. Burnham had little doubt where he did. After serving as a political assistant to lawmaker Tessa Jowell, he longed to enter politics in Westminster, the seat of Britain’s government. “From my early twenties,” he wrote in his memoir, “my ambition was to become a member of Parliament.”

In 2000, Mr. Burnham moved back to his parents’ house to run for office in nearby Leigh.

When he won the election in June 2001, he was just 31 years old.

The Hillsborough legacy

On a spring day in 2009, Mr. Burnham was standing in front of nearly 37,000 people.

It was the 20th anniversary of the Hillsborough disaster, when nearly 100 soccer fans were crushed to death in the deadliest sporting tragedy in British history. In the ugly aftermath, the police and parts of the media falsely blamed Liverpool Football Club fans, hiding the actual cause: failures by the police.

Mr. Burnham, the still-youthful secretary of Culture, Media and Sport, was deeply familiar with the tragedy, not least as one of his friends had been at the Hillsborough match. When he was asked to represent the government at Liverpool’s Anfield stadium for the remembrance, his “blood instantly ran cold,” he later recalled. The government was still, two decades later, refusing to acknowledge what had happened.

As he began to speak, the boos came quickly. The crowd chanted “Justice for the 96” for several minutes, leaving Mr. Burnham to stand silently.

Hillsborough became his cause. Mr. Burnham added his voice to those arguing for a new inquest and full disclosure of all documents related to the disaster. After listening to the debate, Prime Minister Gordon Brown backed Mr. Burnham. Subsequent investigations found the police had lied repeatedly and Liverpool fans were cleared of any responsibility.

The need for an extended fight on behalf of the Liverpool fans was deeply frustrating for Mr. Burnham, according to his memoir and other interviews. He still believed he had a place in London, but only if he could bring wholesale change to the system.

In 2010, Mr. Burnham tried, and failed, to become the leader of the Labour Party. Five years later, he tried again.

He entered the 2015 contest as its front-runner, but was defeated by Jeremy Corbyn, from the party’s hard-left wing.

Disillusioned by that loss and his broader frustration with politics in London, Mr. Burnham announced in 2017 that he would campaign for the Manchester mayoralty. In his memoir, he described the Hillsborough anniversary as the moment he realized how the British political system “fails people in a very personal way.”

“While it would be another eight years before I finally left, things were never the same after that day,” he wrote. “The spell was broken and I had fallen out of love with Westminster.”

Promises in Manchester

On his first day as mayor in 2017, Mr. Burnham declared that he would make good on an audacious promise to end rough sleeping — the British term for homelessness — in three years.

“Whilst the city centre’s skyline is filled with cranes, our streets should not be crowded with people who have no roof,” Mr. Burnham said as he walked through the downtown, greeting people who had spent the night on the street.

It was classic Burnham — the kind of retail politics that he excelled at during his campaign. He pledged to donate 15 percent of his $148,000 salary to homelessness charities, and continued to do this over his nine years in office.

But critics say the rough-sleeping promise was also evidence of another trait: the tendency to over-promise and under-deliver.

In 2020, the year Mr. Burnham had said there would be no more homeless people sleeping in the streets of Manchester, the problem had dropped by about half. But the Manchester Mill reported this year that the number of rough sleepers had increased steadily over the past four years, undermining the mayor’s promise.

Some of Mr. Burnham’s other efforts in Manchester have been more durable.

His relentless pursuit of economic investment has led to a building boom downtown. And while he has little foreign policy experience, Mr. Burnham traveled the globe as mayor, building partnerships with businesses in a way that complicated the idea that he was a traditional left-wing politician.

In September 2018, he traveled to China to boost efforts to improve high-speed trains across his region. Two months later, the Chinese Embassy in Britain posted a news release praising the mayor’s visit.

Mr. Burnham’s most well-known legacy in Greater Manchester is the buses. Using existing mayoral powers, Mr. Burnham dramatically improved the area’s transportation network. He imposed new regulations over the legal objections of private bus companies, lowering fares and increasing reliability.

Luke Raikes, who was a member of the Manchester City Council for 11 years, said the new bus system “made a huge and very visible difference to people.”

Overplaying his hand

The event on the fringes of the 2025 Labour Party conference was packed. Everyone wanted to hear Manchester’s mayor, who had hinted days earlier that he might challenge Mr. Starmer for leadership of the party.

“I’ve done nothing more than launch a debate,” Mr. Burnham insisted that day in September. At the time, he had no path to power. He couldn’t challenge the prime minister unless he was a member of Parliament.

The conclusion in Labour Party circles was that Mr. Burnham had overplayed his hand. His barely concealed ambition suggested he lacked party loyalty.

But eight months later, voters in a set of municipal and regional elections delivered a searing declaration of no confidence in Mr. Starmer, who was already badly weakened by a scandal over Peter Mandelson, a Jeffrey Epstein associate he had appointed as U.S. ambassador.

Mr. Burnham’s moment had arrived.

Within days, a Labour lawmaker in Makerfield resigned to make way for Mr. Burnham to run. In June, he won decisively.

For more than two decades, Mr. Burnham has accused national governments of failing to address the needs of working-class people, especially outside London. At his Covid news conference in 2020, he railed against a Conservative government he accused of refusing to listen to the needs of its people — “people too often forgotten by those in power,” he said that day.

On Monday, he will finally wield that power himself, and will immediately confront some of the difficult choices that he accused others of botching.

“We have no sense of the trade-offs Burnham is going to make,” Mr. Herrmann said. “I would bet my bottom dollar that he doesn’t know what trade-offs he’s going to make either.”

Eshe Nelson contributed reporting.