Chavarat Charnvirakul has resigned as leader of Bhumjaithai and the party will call a meeting to elect his replacement in early October, party spokesman Supachai Jaisamut said on Tuesday.
Mr Supachai made the announcement after today's meeting of Bhumjaithai.
Mr Chavarit, 76, submitted his resignation letter on Aug 29, citing his age as a reason and his wish to see new generation party members run the country's administration.
He will continue to serve as an MP and party's adviser.
Boonjong Wongtrairat, the party's secretary-general, is now acting party leader.
Mr Supachai expected the party to call a meeting to chose the new leader and a new party executive committee early next month.
Sources said the Friends of Newin faction in the party would nominate Anuthin Charnvirakul for the leadership and Saksayam Chidchob, a younger brother of party co-founder Newin Chidchob, for the secretary-general's post.
The other faction led by Somsak Thepsuthin had yet to name its nominees for the posts.