LONDON — Britain has named Karen Pierce, a career diplomat and the country’s current ambassador to the United Nations, as its new ambassador to the United States, the prime minister’s office announced on Friday.
Ms. Pierce succeeds Kim Darroch, who announced his resignation last year after his blunt assessments of President Trump as “radiating insecurity” and the Trump administration as diplomatically “clumsy and inept” were leaked.
Mr. Darroch said he would step down after the release of those comments, saying that the situation had left him in an untenable position. Mr. Trump responded by referring to the ambassador as “wacky,” a “very stupid guy” and a “pompous fool.”
Ms. Pierce, who served as Britain’s representative to the United Nations for less than two years, will take up the position at a crucial time in the so-called special relationship between the two countries.
Britain is laying the groundwork for what it regards as a vital trade deal with the United States after having left the European Union, and Ms. Pierce will find herself in a crucial position during the negotiations.
Prime Minister Boris Johnson has maintained good relations with Mr. Trump, but the American president demonstrated no reluctance to criticize his predecessor, Theresa May, as well as the mayor of London, Sadiq Khan.
Those comments, along with American efforts to prevent Britain from using products from the Chinese electronics giant Huawei in its 5G network, have introduced an element of fragility into the relationship.
“I am honored to have been asked to represent the U.K. in the U.S.,” said Ms. Pierce, who will be the first woman to hold the position, in a statement. “I think it is the U.K.’s single most important relationship. There is a deep bond between Britain and the US, built on many pillars.”
Ms. Pierce is one of Britain’s most experienced diplomats, holding a variety of roles in the diplomatic corps, including postings overseas in Japan, Switzerland and the United States.
She started with the Foreign Office in 1981. Before moving to the United Nations, she was the chief operating officer for the Foreign Office, where she worked for Mr. Johnson, who was foreign secretary at the time and is now the prime minister.