SEOUL, South Korea — Former Defense Minister Shigeru Ishiba on Friday won a race to lead Japan’s conservative ruling Liberal Democratic Party, a victory that puts him in line to succeed resigning Prime Minister Fumio Kishida.

The 67-year-old political veteran is expected to be officially named prime minister in the Diet next Tuesday.

He beat Economic Security Minister Sanae Takaichi, a hardline rightist bidding to become Japan’s first female prime minister, by 215 votes to 194 in a tight run-off among LDP lawmakers. The first round featured a record nine candidates.

---

---

Mr. Ishiba, who has called for an Asian version of NATO, looks like the safest pair of hands to helm Japan, a key U.S. ally in the Indo-Pacific region at a time of mounting tensions with North Korea, Russia and China. With U.S. forces stretched thin globally and regional democracies grouping to push back, Japan, the world’s fourth-largest economy, could be a natural unifier. 

Japanese capital markets rose after Mr. Ishiba’s win.

But there are also questions about whether Mr. Ishiba, who lacks a strong support base inside the LDP, can take a firm grasp of the government, which has suffered from a string of weak, “revolving-door” prime ministers in recent years.

A general election can wait until October 2025, but there were widespread expectations the winner of Friday’s vote would call for an earlier vote.

Though he was the favorite heading into the nine-horse race, Mr. Ishiba looked relieved rather than delighted when he stood and bowed after the result was read out to assembled LDP lawmakers.

With no candidate securing a clear majority in first-round voting, the race went to a head-to-head runoff. That had been expected. What was unexpected was Ms. Takaichi’s clear win in the first round: She garnered 181 votes to Mr. Ishiba’s 154.

Widely regarded as conservative, the LDP is a broad political church: Factions of the party range from middle-of-the-road to hard right.

Some analysts said Mr. Ishiba’s come-from-behind victory was delivered by party moderates, who switched their allegiance in the second round to keep Ms. Takaichi from winning.

The race was prompted by the August decision by Mr. Kishida, battered by low poll ratings and party scandals, to step down.

Mr. Ishiba is a long-time political player who entered the Diet in 1984. Friday’s vote was his fifth try for the top job in the LDP.

He represents Tottori, Japan’s least populated prefecture. Known for his candor, he is more popular with LDP rank-and-file than with lawmakers, whom he has criticized in the past.

“I have undoubtedly hurt many people’s feelings,” he told the LDP Friday. “I sincerely apologize for all of my shortcomings.”

A former LDP secretary general, Mr. Ishiba knows the party’s ins and outs, but it is questionable whether he can get a firm grip on power.

“Ishiba is resented by the mainstream LDP,” said John Nilsson-Wright, who studies modern Japanese politics at Cambridge University. “And there is a sense in some quarters that his views on the economy are unsophisticated, and therefore problematic.”

He has questioned Japan’s reliance upon nuclear energy, though he has wavered on that issue.

Mr. Ishiba is firmer on defense. He served as director general of the Japan Defense Agency from 2002 to 2004 and as minister of defense from 2007 to 2008.

A hobbyist military modeler, he has argued that Japan should strive for “nuclear latency” — not building a nuclear bomb but maintaining the civilian capacity to swiftly create one should the need arise.

During the campaign, Mr. Ishiba raised eyebrows by suggesting an Asian NATO, a multilateral, mutual-defense network of fellow democracies, an idea Mr. Nilsson-Wright dismissed as “hopelessly unrealistic” and which U.S. experts have called premature.

Still, Mr. Ishiba has been ahead of the curve before.

In 2010, he called for a new force of Japanese marines to defend its far-flung southern islands. As China’s regional assertiveness increased and Tokyo refocused on defense, an amphibious brigade was created in 2018.

His stance for a more assertive Japan that is less reliant upon the U.S. might win nods in Washington, but he has also criticized President Biden’s efforts to Japan’s Nippon Steel bid for U.S. Steel on national security ground, calling it “unsettling” that Japan is considered a risk to American economic security and that the policy “could undermine trust.”