Former defence minister Shigeru Ishiba will become Japan's next prime minister after winning the ruling party's leadership vote on Friday, the official count showed.

Ishiba, 67, beat hawkish Sanae Takaichi, who would have been the country's first ever woman leader, in a run-off.

His successful leadership bid after four failed attempts puts the self-confessed lone wolf at the helm of a Liberal Democratic Party that has ruled Japan for most of the past seven decades.

Ishiba takes over with the party in crisis, having seen its public support ebb away over the past two years with revelations of links to a church branded a cult by critics and a scandal over unrecorded donations.

A former defence minister who entered parliament in 1986 after a short banking career, Ishiba was sidelined by outgoing prime minister, Fumio Kishida, becoming instead a dissenting voice in the party.

He has rebelled on policies including the increased use of nuclear energy and has criticised his party for not allowing married couples to use separate surnames.

"I consider this my final battle," Ishiba said last month when he launched his campaign at a Shinto shrine in rural Tottori prefecture, where his father was governor and where Ishiba began his political career at the height of Japan's fast growing bubble economy.

"I will bring back a vibrant Japan where people can live with a smile."

Ishiba, who has also served as agriculture minister, promised to move some ministries and government agencies out of Tokyo to help revive Japan's moribund regions. He has also proposed establishing an agency to oversee the construction of emergency shelters across disaster-prone Japan.

Seen as an LDP intellectual heavyweight and expert on national security policy, he advocates for a more assertive Japan that can reduce its reliance on longtime ally, the U.S., for its defence.

That position, analysts say, could complicate relations with Washington. (Reuters)