Despite leading his party to big losses in a snap general election last month, Shigeru Ishiba, the prime minister of Japan, won a vote in Parliament on Monday to carry on as the country’s leader.

Mr. Ishiba, whose Liberal Democratic Party lost its parliamentary majority for the first time in 15 years, will effectively lead a minority government.

The result puts Mr. Ishiba in a precarious position as his government continues to deal with the aftermath of a political finance scandal, along with inflation, labor shortages and the increasing burdens of an aging population. Analysts said Mr. Ishiba could struggle to survive in the long term, putting Japan at risk of returning to a revolving door of prime ministers just as it prepares to grapple with increased unpredictability in the United States, its most important international ally, following the re-election of Donald Trump as president.

In a runoff election with the leader of the Constitutional Democratic Party, Japan’s largest opposition group, Mr. Ishiba defeated Yoshihiko Noda, a former prime minister, 221 to 160. Mr. Ishiba was first elected prime minister in September.

Although the Constitutional Democrats made significant gains in last month’s election, they did not win a majority in the lower house of Parliament, which would have given them the right to select the prime minister. With seven other small opposition parties fielding leadership candidates, Mr. Noda could not amass enough unified support to unseat Mr. Ishiba.

With nearly one in five members of the lower house declining to cast a vote for either candidate in the runoff, Mr. Ishiba has a fragile hold on power.