Gen Prayut Chan-o-cha has invoked Section 44 of the 2014 interim charter to strip Thaksin Shinawatra of his police rank, effective on Sunday.
The general signed the 26/2558 National Council for Peace and Order (NCPO) order in his capacity as the NCPO chief. It was published on the Royal Gazette website on Saturday.
A source said Gen Prayut apparently chose to invoke his power under Section 44 instead of seeking His Majesty the King's endorsement as is the regular channel, possibly to protect the palace from a political backlash.
But critics have said the use of Section 44 was probably to prevent future lawsuits as the power under this clause is absolute.
Even deputy government spokesman Werachon Sukondhapatipak said on Friday the prime minister would seek His Majesty's approval to remove Thaksin's rank.
The order stated the Royal Thai Police had proposed removing the rank of Pol Lt Col Thaksin Shinawatra after he had been sentenced guilty in a final judgement and was charged in several other criminal offences, a disgrace to the service.
"The chief of the NCPO, with authority under Section 44 of the 2014 interim constitution and with the approval of the NCPO, after careful consideration, found it affects national security and necessitates urgent action.
"Having verified legal issues based on the Royal Thai Police's regulation on rank removal and the facts, the NCPO chief found the case had ground and decided to exercise the NCPO authority to issue the order to remove Pol Lt Col Thaksin Shinawatra of his rank based on the National Police Act B.E. 2547.
The order takes effect a day after it is announced in the Royal Gazette.