The date was set after the Constitutional Court on August 16 rejected requests to review a parliamentary decision that rejected Move Forward Party leader Pita Limjaroenrat from being renominated as prime minister.
Wan Muhamad told reporters that he and Senate President Pornpetch Wichitcholchai agreed on the date.
Thailand's constitution stipulates that to become the prime minister, a candidate needs to receive the support of a majority of 750 members of the Senate and the House of Representatives or at least 376 votes. A candidate for the prime minister must not be a member of parliament.