The UK elects a no-drama prime minister after years of post-Brexit chaos

Starmer, a former public prosecutor, put an end to all of that. He dragged the party to the center, rooted out members who expressed antisemitic attitudes, and two years after taking charge instructed Labour members to sing “God Save the King" during the party’s annual meeting. The only flags in the hall were Union Jacks.

Now, eight years after the U.K. voted to leave the European Union and entered an era of political and economic turmoil, British voters have asked the man known as “No-Drama Starmer" to steady the entire country with his brand of dull competence.

Starmer will become Britain’s prime minister after his Labour Party on Thursday secured one of the biggest majorities in its history, winning a projected 411 seats out of 650 in Britain’s Parliament. The Tories, meanwhile, slumped to their lowest vote share in modern history.

The scale of the landslide victory was just shy of Labour’s biggest previous win in 1997 under Tony Blair, who also ended a long period of Conservative rule by pushing his party to the center, inaugurating a period of 13 years in power, the longest Labour has ever governed.

Unlike Blair, however, the 61-year-old Starmer isn’t charismatic, isn’t offering a vision of sweeping change, and isn’t even particularly popular. Polls regularly show that slightly more voters disapprove than approve of him. Even his most ardent supporters say he owes his victory as much to the implosion of the Conservative Party as he does his own political transformation.

Yet voters flocked to Starmer as a salve for post-Brexit chaos. In the course of five months in 2022, Britain had three different prime ministers and a financial run on the pound. Former Prime Minister Boris Johnson was kicked out by his own party after repeated scandals, including throwing parties at 10 Downing Street during the pandemic lockdown and misleading Parliament.

At a time when populist far-right parties are on the rise in Europe, and American politics is dominated by the presence of Donald Trump, Starmer will test whether citizens respond to someone who offers pragmatism over soaring rhetoric, sweeping promises and populism.

“Politics is littered with people who shout very loudly about a problem," Starmer said a few years ago. “There is a different type of passion…which is to say, ‘What is the answer to that problem?’"

As a law student at Oxford, Starmer helped edit a Trotskyist magazine called “Socialist Alternatives." His peers don’t remember him for what he wrote, but rather the fact that he made sure the magazine was printed and handed out. Later on, as Britain’s chief prosecutor, he put terrorists in jail—but listed one of his biggest achievements as moving the criminal justice system from paper to digital. As Labour’s leader his first act was tweaking arcane party bylaws to tighten his control over how policy was set.

Starmer is the antithesis of Johnson, the last leader Britain elected back in 2019. The charismatic Johnson was the product of an elite private school, sported wild blond hair, quoted Latin and painted a sweeping vision of “uplit sunlands" under Brexit. Starmer is from a modest background, wears glasses and a neat side part, doesn’t have a favorite novel, is a wooden public speaker, and pitches himself as a man who can make tough choices in difficult times.

Britons are impatient for change. The U.K. economy has only grown an average of 1.3% during the years since 2016, and real wages have stagnated in recent years. The country has 6.3 million people waiting for treatment on its state-run National Health Service. Public finances are constrained after doling out billions to the public during the pandemic and an energy crisis caused by the Ukraine war. Prisons are so full that criminals may have to soon be released early.

Starmer spent most of the campaign underscoring what he won’t do: raise taxes broadly or sharply boost spending, because he says Britain can’t afford it. Instead, his pledges are a five-point plan that includes cutting red tape to build more houses, reducing immigration, creating a fund to accelerate the build-out of green-energy infrastructure, and making it easier for people to get appointments in the health system.

On foreign policy Labour is also promising continuity, keeping the U.S. close and supporting Ukraine. He says he is pro-business and wants to patch up relations with Europe but not reverse Brexit.

Not a politician

Starmer is something of an oddity in Westminster. He is rarely seen in Parliament’s bars and isn’t famed for lyrical oration. It’s nearly unheard of for a British politician with so little experience in politics to win a general election, says Robert Hayward, a pollster and Conservative member of the House of Lords. Starmer only entered politics nine years ago. “He doesn’t know the Labour Party," he said. “He is coming from the outside."

Interviews with a dozen people who have worked with Starmer paint a picture of a toiler who has used meticulous grind to achieve results. He leans into his reputation. When a man on the campaign trail asked him why he was so dry, Starmer drew laughs by replying, “Cheers mate!"

He also has a ruthless streak and has proven himself unafraid to jettison allies or policies. After the 2016 Brexit referendum, he spent years campaigning to stop Britain leaving the EU. Running for Labour’s leadership in 2020, he positioned himself as an ally to the left, pledging to nationalize Britain’s energy sector and remove college tuition fees. He called Corbyn a friend.

Within months of becoming Labour leader he threw out those policies, suspended Corbyn from the party and accepted Brexit. In the past year alone, he scrapped a long vaunted £28 billion a year green investment plan, and watered down a policy to improve workers’ rights. It has turned him into a hate figure for the far left of the party, and left many traditional Labour voters unenthusiastic about him.

“The man is a barefaced liar," says James Schneider, who was in charge of Labour’s communications under Corbyn.

Others say it’s simply Starmer’s evolution toward the center.

“He’s espoused some quite left-wing views," says Andrew Cooper, who went to school with Starmer and previously advised former Tory Prime Minister David Cameron. “But along the way, what he’s acquired is the sort of understanding that drove the Blair government, which is that there isn’t any point in having progressive principles if you don’t win."

Starmer grew up in modest circumstances just south of London in a place called Oxted, an affluent suburb and Conservative heartland. His parents named their son after the Labour Party’s founder, Keir Hardie. His father was a toolmaker and devoted himself to caring for Starmer’s mother, a former nurse who suffered a rare form of inflammatory arthritis that left her struggling to walk. He became the first person in his family to graduate from university.

After school, Starmer embarked on a career as a libertarian human-rights lawyer. He gained plaudits for representing people who faced the death penalty in the Caribbean and Africa, winning several landmark cases including one that helped overturn the mandatory death penalty in Uganda.

He worked pro-bono for nearly a decade defending two vegetarian activists whom McDonald’s sued for libel after they distributed leaflets criticizing the company. The “McLibel" case was only partially successful: McDonald’s won damages but suffered a hit to its reputation.

One of his clients was a man who calls himself Arthur Pendragon, a modern-day druid who claims to be the reincarnation of King Arthur. Pendragon had been barred from trying to celebrate the summer solstice at Stonehenge. Starmer took the case, pro bono, to the European Court of Human Rights and the druid was eventually allowed to gather at the famous stones. “He was so good the government bought him off and gave him a job," says Pendragon.

In 2008, Starmer became the U.K.’s director of public prosecutions. He spent nine months visiting all 42 of the prosecution service’s regional offices. Its budget was cut by around a third as the ruling Conservative government sliced public spending to patch up the government’s finances.

Starmer said he felt the scale of the spending cuts risked damaging the foundations of the British welfare state created in the wake of World War II. Already in his 50s, he entered politics as a Labour lawmaker.

Rooting out antisemitism

The Labour Party was born in 1900 out of the trade-union movement. By the 1990s the party had reinvented itself as a center-left grouping under Blair. But following the 2007-08 financial crisis, and a new rule that allowed nonmembers to pay a small fee and vote for the Labour leader, a wave of mainly young, left-wing members poured into the party and lifted Corbyn, a bearded socialist, to its helm in 2015.

While many Labour lawmakers refused to serve under Corbyn, Starmer entered Parliament in 2015 and worked in his shadow cabinet.

Starmer campaigned for Corbyn during a 2019 election, during which Labour pitched a four-day workweek and the nationalization of the country’s broadband infrastructure. Corbyn, who once described members of Hamas and Hezbollah as “friends," had allowed thousands of complaints of racism by Jewish Labour members to go unresolved. The problem was so bad that Britain’s chief rabbi publicly warned of a “poison" infecting the Labour movement. (Corbyn denies he is antisemitic and has apologized for calling the people linked to the militant groups as friends).

Voters balked and Labour slumped to its worst defeat since 1935.

Within three days of becoming Labour leader, Starmer organized a video meeting with Jewish representatives and apologized. Starmer, whose wife is of Jewish heritage, said it was a moral imperative to fix the problem and the British electorate would never vote for a party with a reputation for racism.

Starmer promised the group that all the cases of alleged antisemitism would be placed on his desk by the end of the week, according to people on the call.

“I think if you take the antisemitism issue as a bellwether exam you can see that he’s a man who is determined to carry out what he says he will do." says Jonathan Goldstein, the co-owner of Chelsea soccer club, who was on that call with Jewish representatives back in 2020. Goldstein says he has now rejoined the Labour Party.

After a Equality and Human Rights Commission report concluded that Labour had broken the law by indirectly discriminating against Jewish members, Corbyn said the scale of the problem was “dramatically overstated" by opponents. Starmer suspended him. He then fired a lawmaker from his shadow cabinet after she liked a tweet containing an antisemitic conspiracy theory and refused to delete it.

In the ensuing months dozens of staff were hired to go through complaints, party rules were changed to make it faster to discipline Labour members, and hundreds were kicked out of the party.

After the Oct. 7 attacks on Israel, Starmer said Israel had a right to self-defense. Earlier this year, ahead of a special district election, a Labour candidate was caught saying Israel had “allowed" the Hamas attacks as a pretext to invade Gaza. Starmer pulled support for the candidate and Labour lost the seat, but said he had no regrets.

Starmer’s tenure nearly came to a quick end. In 2021 the party lost a special election in Hartlepool, a Labour heartland, to the Conservatives, which nearly prompted him to quit, aides say.

Starmer’s aides looked to other social democrats across the world for inspiration. They saw how the Biden campaign had succeeded against Trump in 2020 by promising an alternative to chaos. In Germany and Australia, staid center-left politicians, Olaf Scholz and Anthony Albanese, had won victories running tightly disciplined, unshowy campaigns, says Claire Ainsley, who was Starmer’s executive director of policy and now works at the U.S.-based Progressive Policy Institute.

“We needed to target towns and suburbs around the country," she said. “We couldn’t just be the party of metropolitan voters in the big cities." That meant ditching a lot of progressive policies to attract back working class voters and present themselves as a party which respected national security and business, she says.

There were question marks over whether Starmer had the persona to sell Labour to the public. For years, Starmer refused to talk much about his background. He is fiercely protective of his two children, whom he still won’t name in public to protect their privacy, and his wife, who works for the National Health Service. Yet because he is referred to in the British press as “Sir Keir," on account of his knighthood in 2014, and lives in an upmarket part of London, many voters assume he is a rich liberal lawyer.

In 2021, former President Barack Obama advised Starmer to be more open about his upbringing to better connect with voters. Starmer began mentioning in nearly every interview that his father was a toolmaker and mother was a nurse.

Not long after the rocky period when former Tory Prime Minister Liz Truss quit after an historically short tenure amid a selloff of the pound, Starmer was asked if the time was right for Mr. Boring?

“I think what they want is a serious politician," Starmer said. “A serious prime minister."

“So that’s a yes?" the interviewer asked.

“Yes," said Starmer.

Write to Max Colchester at Max.Colchester@wsj.com