The 2021–22 season is Ratchaburi Mitr Phol Football Club's 15th existence.

Also, having finished 4th in the first half of 2020-21 Thai League 1, Ratchaburi Mitr Phol Football Club are qualified for the play-off stage of the 2021 AFC Champions League for the first time in the club's history, but after Jiangsu ceased operation,[1] Ratchaburi Mitr Phol automatically qualified to the group stage instead alongside Pohang Steelers.

2021–22 Thai League 1 season was supposed to start on 31 July 2021 and concluded on 21 May 2022.

[3] Then, due to the situation of the COVID-19 pandemic is still severe, FA Thailand decided to postpone the season to start on 13 August 2021 instead.

Therefore, FA Thailand decided to postpone the opening day for the second time to start on 3 September 2021.