Buriram United were the defending champions, having won their Thai Premier League title the previous season.
Nakhon Ratchasima, Saraburi and Navy entered as the three promoted teams.
Police United, PTT Rayong, Songkhla United, Air Force Central and GSE Samut Songkhram were relegated to the 2015 Thai Division 1 League after finishing the 2014 season.
They were replaced by the best three teams from the 2014 Thai Division 1 League champions Nakhon Ratchasima, runners-up Saraburi and third place Navy.
Note: Flags indicate national team as has been defined under FIFA eligibility rules.