Yohei Kono, former president of the Liberal Democratic Party, will be appointed as Speaker of the House of Representatives.
The appointment will be made during a special Diet session expected to be convened next week, LDP executives said Wednesday.
Candidates are traditionally elected from the party that holds the most seats in the chamber.
Prime Minister Junichiro Koizumi proposed the idea at a party executive meeting Tuesday evening. His idea was immediately approved by the attendants, LDP Secretary General Shinzo Abe said.
Kono, 66, has informally consented to the proposal, Abe said.
Kono, a former foreign minister, is the only LDP president who failed to become prime minister since the party's establishment in 1955.
During his tenure between July 1993 and Sept. 1995, non-LDP prime ministers Morihiro Hosokawa, Tsutomu Hata and Tomiichi Murayama were in office.
Kono, now in his 13th term since 1968, has held a number of key positions, including chief Cabinet secretary and vice prime minister. He now heads a minor intraparty faction of the LDP.