Britain’s New Prime Minister Kier Starmer Is About to Get a Crash Course in Statecraft

Prime Minister Keir Starmer of Britain will barely get his feet under the desk in 10 Downing Street before he flies to Washington this coming week to attend a NATO summit. A week after that, he will play host to 50 European leaders at a security meeting at Blenheim Palace, the birthplace of Winston Churchill.

It’s a crash course in global statecraft for Mr. Starmer, Britain’s first Labour prime minister in 14 years. But it will also give him the chance to project an image of Britain that is uncharacteristic in the post-Brexit era: a stable, conventional, center-left country amid a churning tide of politically unsettled allies.

In Washington, Mr. Starmer will encounter President Biden, who is resisting calls to abandon his race for re-election because of age-related decline. He will meet with President Emmanuel Macron, whose attempt to fend off the far right in France appears to have backfired, and with Chancellor Olaf Scholz of Germany, whose coalition has been weakened by the advance of the hard right in European Parliament elections.

Mr. Starmer’s success with Labour may raise hopes among some that Britain’s embrace of a center-left party could be replicated in France and the United States. But it is equally plausible that Britain could be a harbinger of something else: an anti-incumbent revolt and simmering populism, embodied in Britain by the insurgent Reform party, that could play out elsewhere. That was the case in 2016, when voters backed the Brexit referendum six months before the United States elected Donald J. Trump.

Britain’s shift to Labour, analysts pointed out, was not about ideology so much as about fatigue with a Conservative government and distrust of political institutions in general. That same fatigue exists in France, under an unpopular centrist president, and in the United States, under an aging Democratic one.

For now, however, diplomats said that Mr. Starmer’s remarkable election victory would give him a sheen of political stardust with his fellow leaders, for whom such victories have been in short supply lately.

“The huge victory means that he’ll be mobbed at the NATO summit,” said Kim Darroch, who served as Britain’s ambassador to Washington. “Everyone will want to talk to him; everyone will want a selfie with him.”

Depending on how the American presidential election goes, Mr. Starmer could someday even find himself in a position not unlike that of another German chancellor, Angela Merkel, who was viewed as a bulwark of the rules-based international order when Mr. Trump was president.

For Mr. Starmer to assume that mantle, however, he will have to find a way to jump-start Britain’s economy, according to Mr. Darroch. Diplomatic power correlates with economic power, and Britain’s anemic economy — combined with its decision to leave the European Union — has diminished the country’s role in international affairs.

Mr. Darroch also said that Mr. Starmer should overcome his reputation for caution and try to do something bold with Europe. He has ruled out rejoining the bloc’s vast single economic market, since that would mean allowing people from Europe the freedom to live and work in Britain, or its customs union, which would mean accepting some of the bloc’s rules on tariffs and duties.

Any significant deal would involve difficult trade-offs, but Mr. Starmer, who opposed leaving the European Union, does not carry the baggage of Conservative predecessors like Boris Johnson, who fronted the Brexit campaign and cultivated a reputation as someone who relished a scrap with Europeans.

“They haven’t been insulted by Labour the way they were by the Tories,” said Mr. Darroch, who also served as Britain’s permanent representative to the European Union. “He doesn’t have that legacy; he doesn’t have that baggage.”

Mr. Starmer traveled widely abroad when he was a human rights lawyer. But his expertise does not lie in foreign policy, and during the election campaign, he mainly sought to avoid significant daylight with the Conservative government on the two major issues of the day: the wars in Ukraine and Gaza.

Mr. Starmer has pledged to maintain Britain’s military support of Ukraine, which has enjoyed broad public backing from the start of the war. As Labour Party leader, he worked hard to shake off a reputation for hostility to NATO and suspicion of the military that had taken root under his predecessor, Jeremy Corbyn.

“One of the things that was disastrous under Corbyn is that he didn’t have a commitment to NATO, he didn’t have commitment to defense, and people didn’t like that,” said Robert Ford, a professor of political science at the University of Manchester.

Israel and Gaza pose a trickier issue for Mr. Starmer. He has called for a cease-fire in the conflict, but he took awhile to get there, which angered those on the left wing of his party, as well as Muslim supporters of Labour.

The electoral reverberations were greater than expected. Jonathan Ashworth, a Labour lawmaker who was likely to be appointed to Mr. Starmer’s cabinet, unexpectedly lost his seat in the Leicester south district to Shockat Adam, an independent who declared, “This is for the people of Gaza,” during his victory speech.

Even Mr. Starmer’s share of the vote in his own North London seat reduced by 17 percentage points compared with the election in 2019, in part because of a challenge by an independent who voiced anger with Labour’s stance on Israel and the war in Gaza.

Israel may continue to vex Mr. Starmer, much as it has Mr. Biden and Mr. Macron. Both faced criticism for sticking too long with Prime Minister Benjamin Netanyahu of Israel and for not more forcefully condemning Israel’s conduct of the war in Gaza.

David Lammy, who was appointed foreign secretary by Mr. Starmer on Friday, described his boss’s approach to the war as shaped by his background as a human rights lawyer. He said in an interview in April that Mr. Starmer would continue to support Israel but demand that it comply with international law.

“The situation in Gaza is a description of hell on Earth,” Mr. Lammy said. “Man-made famine, no significant medical assistance at all, people eating cactus. The Labour Party has played the best role it could as an opposition party.”

Mr. Lammy has said that a Labour government will fuse progressive values with a realistic approach to the world — a formula he called “progressive realism.”

“There was a lot of magical thinking in the Boris Johnson, Theresa May, Liz Truss, Rishi Sunak period,” Mr. Lammy said, referring to the four Conservative prime ministers who preceded Mr. Starmer. “And a harking back to an era long gone, and not enough focus on today’s challenges.”