How Britain’s Keir Starmer became Europe’s soft-spoken Trump whisperer

The dinner would set the tone for an unusual political relationship between the brash American president and the soft-spoken, left-of-center former human-rights lawyer. Trump dimmed the lights to show Starmer the sparkling Manhattan skyline, and expressed his deep love for England and Scotland over a two-hour dinner, according to a senior U.K. official.

Another factor may have helped win Trump over: Starmer wasn’t meeting during his trip with Trump’s opponent, then-Vice President Kamala Harris.

Ever since, Starmer has been leveraging Trump’s appreciation for the U.K. Along the way, the bookish prime minister has perfected the art of handling the mercurial president, a playbook that other European leaders have since broadly copied: Be polite, don’t voice disagreements publicly and on the whole do what he asks. You might score some wins yourself.

So far it is paying dividends. Britain secured an early trade deal with the U.S. and has successfully petitioned Trump to not turn his back on Ukraine. Ahead of Trump’s state visit to Britain, U.S. tech firms including Microsoft and Nvidia announced over $42 billion of investment into the U.K. as part of a tech partnership between the two nations. This trans-Atlantic relationship has proved an unexpected bright spot for Starmer, who has tanked in the polls in Britain amid stagnant economic growth and rising illegal immigration.

“Starmer has been quite astute in assessing areas where he has some influence, and others where he will have to accept a Trumpian worldview," says Sophia Gaston, a foreign-policy expert at King’s College London.

The relationship—forged by what officials say is the president’s genuine fondness for the British Labour Party leader—was further cemented Wednesday at a lavish state dinner at Windsor Castle. The pair are due to have a bilateral meeting Thursday to discuss other issues including trade. Before leaving Washington, Trump suggested he was open to making some concessions to Britain on trade.

The president regularly calls Starmer, sometimes unprompted late at night, officials say. Starmer drops what he is doing to hear Trump out. The president thinks Starmer holds his ground on his positions without being critical of Trump’s views, according to a senior administration official. Starmer, a process-driven former prosecutor, sees it as a key part of his job to keep the president onside.

Some of this success is down to the two leaders’ personalities. “Starmer conveys a sense of British formality and values without a condescending or imperious tone," says Gaston. This is in contrast to the more forthright approach taken by other European leaders such as France’s Emmanuel Macron.

The British Trump playbook has downsides, of course. Britain agreed to a major hike in defense spending at a time when government finances are stretched, and swallowed tariffs without imposing retaliatory measures. The question now is what happens if Trump continues to press for more on issues such as free speech, which has seen the U.K. heavily criticized by some in the MAGA movement, or conditions for the U.S.’s continued support for Ukraine.

Starmer has also indicated he will support recognizing Palestinian statehood, a move that top Trump officials have criticized.

“It may be that a certain point for Starmer not pushing back or hitting against Trump is a political liability for him, and he feels the need to do it," says Max Bergmann, director of the Europe, Russia, and Eurasia Program at the Center for Strategic and International Studies.

A key plank in the U.K. government strategy in dealing with Trump was to move fast while the Trump team began to implement its plan to reshape both American trade and foreign policy. This was behind Starmer’s decision in February to quickly hand Trump a second historic state visit to Windsor Castle, playing on the president’s well-known appreciation of the British royal family.

British Prime Minister Keir Starmer and his wife, Victoria, left, and President Trump and first lady Melania Trump, right, joined King Charles III and Queen Camilla at Windsor Castle on Wednesday.

Starmer understood that Trump was eager to announce trade deals, so he acted quickly and benefited from some first-mover advantages, officials say. He negotiated a carve-out for luxury car companies and special treatment for steel and aluminum tariffs. The prime minister also gave in to some of the Trump administration’s biggest asks, including relaxing rules for agricultural imports from the U.S.

The U.K. secured a 10% baseline tariff, below the 15% imposed on the European Union. In some products, the U.K. will pay a higher rate, but it got a discount in key areas like steel and cars. “I expect, across the board, that the U.K. will maintain one of the most beneficial trading relationships compared to any other U.S. trading partner," said Kelly Ann Shaw, a former senior Trump administration trade official.

This summer, the prime minister had no qualms in traveling to Trump’s Scottish golf club to listen to the U.S. leader talk at length about the refurbishment of his resort. When Trump summoned Ukrainian President Volodymyr Zelensky to the Oval Office at short notice in August, Starmer abandoned a vacation in Scotland to fly to Washington and join in. In Canada this year, Starmer literally bent the knee, rushing to pick up documents containing details of the two countries’ trade talks after Trump dropped them in front of reporters.

In private, Trump, who frequently goes on long rants about windmills, also likes to joke with Starmer about the U.K.’s support for wind energy, the senior administration official said.

A glimpse of that dynamic was on display at the two leaders’ meeting in Scotland in July. Sitting next to the president at his golf club, Starmer listened to Trump complain about windmills killing birds, but he didn’t offer a defense of wind projects in the U.K. “We believe in a mix," he said.

Write to Tarini Parti at tarini.parti@wsj.com and Max Colchester at Max.Colchester@wsj.com