The league was suspended last month after four games due to the COVID-19 pandemic.
The FAT and clubs recently agreed that the league will resume in September but certain teams wanted the tournament to restart from scratch.
However, after a vote, they have unanimously agreed that the league should restart from the fifth round of matches, FAT president Somyot Poompunmuang said in a statement.
The top two leagues will from now begin in September and end in May on a permanent basis, he said.
Also, the top-four teams in Thai League 1 at the end of the first half of this season will represent the country in the AFC Champions League, Somyot said.
After four games, Bangkok United and Ratchaburi are joint leaders with 12 points, followed by Port and BG Pathum on 10 points.
There will be two two-week transfer windows before each half of the season.
Clubs have also unanimously agreed to cut their players and employees’ salaries by 50%, according to Somyot.