[3] Thirachai started duty in the 2nd Infantry Regiment, Queen Sirikit's Guard knowns as Burapha Payak (Eastern tigers).

Then in 2015 he was appointed as Commander-in-chief of the Royal Thai Army inheriting the position from General Udomdej Sitabutr.

During 2014 Thai coup d'état, He was commander of the peacekeeping force of National Council for Peace and Order.

[4] He used to go to work in the field in the three southern border provinces as the commander of the Narathiwat Special Task Force.

[5] In December 2016 he was appointed to the Privy Council by King Vajiralongkorn, but was relieved of his duties in June 2018 for unspecified reasons.