Gen Prayuth, also head of the National Council for Peace and Order (NCPO), made the announcement at the NCPO meeting this morning.
Gen Prayuth said he was due to meet HM the King at Klai Kangwon Palace in Prachuap Khiri Khan province at 5pm.
The interim Constitution would set out how the country would be governed in the run-up to a general election.
The military took power on May 22 to restore order in the country after months of turmoil and political protests in a bid to topple former Prime Minister Yingluck Shinawatra.
The military said a general election could be held next year.