Japan's Liberal Democratic Party (LDP) is set to vote on the successor for Prime Minister Shinzō Abe on September 14.
Abe stepped down as Prime Minister last week, citing ill health.
The 65-year-old, who suffers from ulcerative colitis, is to receive new and more prolonged treatment.
He is set to be replaced soon, with the race to elect a successor starting on September 8, as reported by Kyodo.
The vote is due to take place on September 14, with the winner of the election possibly announced on September 16.
It has been decided to hold the leadership election without rank-and-file party members, with ballots cast only by lawmakers and delegates from the LDP's local chapters.
It is hoped this will simplify the process to find a successor amid the coronavirus pandemic and preparations for next year's Olympic and Paralympic Games in Tokyo.
A Kyodo survey found Shigeru Ishiba, Abe's sole rival during the last Prime Ministerial election, was the most popular choice to be the next leader with 34.3 per cent of votes cast.
Chief Cabinet Secretary Yoshihide Suga gained 14.3 per cent, Defence Minister Tarō Kōno 13.6 per cent, Environment Minister Shinjirō Koizumi 10.1 per cent and LDP policy chief and former Foreign Minister Fumio Kishida 7.5 per cent.
The nature of the election will be a setback for Ishiba, however, who is popular among the public but lacks broad support among LDP members.
Whoever is chosen to be Prime Minister will have the hard task of organising Tokyo 2020 during a global health crisis.
Abe has been Japan's Prime Minister since 2012 and heavily backed Tokyo's bid to host the Games.
The Japanese capital was awarded hosting rights at the 125th International Olympic Committee (IOC) Session in 2013, with Abe speaking at the event in Buenos Aires to address members and allay fears over the Fukushima nuclear accident.
At the Rio 2016 Closing Ceremony, he appeared dressed as the popular Nintendo character Mario in one of the evening's most memorable moments.
As the coronavirus crisis came to dominate the build-up to the Games, it was Abe and IOC President Thomas Bach who agreed to postpone the event until 2021.
Bach, International Paralympic Committee President Andrew Parsons and Tokyo 2020 President Yoshirō Mori have all thanked Abe for his role in organising the Games and wished him a swift recovery.