Kemi Badenoch became the Conservatives' new leader and the first Black woman to a head a major British political party on Saturday, after winning a leadership contest on a promise to return the party to its founding principles.

Ms. Badenoch, 44, whose parents were immigrants from Nigeria, becomes the first Black woman to head a party that has had three other female leaders — Margaret Thatcher, Theresa May and Liz Truss. She succeeds Rishi Sunak, who became the first nonwhite British prime minister after taking over the Tories, Britain’s oldest party, in 2022.