Sanae Takaichi, a hard-line conservative Japanese lawmaker, won a critical leadership vote on Saturday, putting her on track to become Japan’s first female prime minister, a milestone in a country where women are vastly underrepresented in politics.

Ms. Takaichi, 64, emerged as the winner of an election by the ruling Liberal Democratic Party after two rounds of voting by lawmakers and rank-and-file members.

She will succeed Shigeru Ishiba, Japan’s prime minister, who announced last month his intent to resign after less than a year in office, with his party being battered in the past two elections that saw it become a minority in both houses of the parliament, known as the Diet.

Ms. Takaichi beat out four other candidates, including Shinjiro Koizumi, the 44-year-old agricultural minister who was seen as the favorite heading into Saturday’s election. She was an ally of Shinzo Abe, the former prime minister assassinated in 2022.