Former Liberal Democratic Party Secretary-General Shigeru Ishiba will officially announce his candidacy for LDP president in September.
Ishiba is expected to make his run official at a news conference on Friday afternoon. He has said he wants to restore the public's trust in politics.
Prime Minister Shinzo Abe has indicated his intention to run for a third term as party chief, making balloting likely to take place for the first time in 6 years.
Ishiba says candidates should make an effort to clearly lay out their views and how they differ if they aspire to be party president and Japan's prime minister. He expressed his desire to hold a substantial debate on policies and party management with Abe.
As of Thursday, all 7 of the LDP's intraparty factions have decided who to support in the race, with 5 of them saying they will back Abe.
In addition to the support from the 5 factions, Abe has apparently secured the backing of Lower House members of the faction led by LDP General Council Chairman Wataru Takeshita. The Takeshita faction has decided to allow its members to vote freely.
Meanwhile, Ishiba will be supported by most Upper House members of the Takeshita faction and his own faction.
Both camps are now stepping up efforts to garner support from lawmakers who do not belong to any faction, as well as rank-and-file party members across the country.