Thailand's coup-making prime minister Prayut Chan-O-Cha bade farewell to the military at a formal ceremony Monday as he prepares to retire as army chief and bed in as a civilian leader.

Prayut, 60, who toppled the elected government of Yingluck Shinawatra in May, retires from military service on Tuesday after a near four-decade career with the coup-prone army.

He will however retain extensive powers as the prime minister and head of the junta -- the National Council for Peace and Order -- whose authority has been guaranteed by an interim constitution.

The new army chief, General Udomdej Sitabutr, is a Prayut loyalist who will step up from deputy army chief on Wednesday.

"During my 38 years, I'm proud of every day of service," Prayut said after an elaborate military parade marking the retirement of a few hundred senior officers.

"From now on I will step back (from the army) and take care of moving the country forward," he added.

Prayut is a staunch royalist who has waded into Thailand's political turmoil on several occasions -- justifying his actions as a defence of the nation and its revered monarchy.

The tough-talking Prayut had to retire at the end of this month from the post of army chief which he has held since 2010.

He is often described as the architect of a May 2010 army crackdown on a months-long rally of "Red Shirt" opposition supporters in Bangkok. The crackdown left scores dead.

Red Shirts are loyal to billionaire former prime minister Thaksin Shinawatra, who was ousted in an earlier coup in 2006 and lives in self-exile to avoid jail for a graft conviction.

Thaksin's supporters, drawn from the rural north and northeast and the urban poor and middle classes, say his only crime is to rattle the Bangkok-based establishment -- which is backed by the army and elements of the judiciary -- with his massive electoral popularity.

Prayut, who has stacked his cabinet with military top brass, is set to travel to Myanmar on October 9 in his first overseas foray as premier.