Assistant army chief Thirachai Nakwanich has been appointed as the new army chief in a military reshuffle endorsed by His Majesty the King.
The list, published in the Royal Gazette on Friday, will see Gen Thirachai succeed Udomdej Sitabutr, who retires at the end of September.
Preecha Chan-o-cha, younger brother of Prime Minister Prayut and another assistant army commander, becomes the defence permanent secretary.
Thirachai: Succeeds Gen Udomdej
Gen Thirachai was believed to be the favoured choice of Defence Minister Prawit Wongsuwon since Gen Thirachai's career has followed a similar path to his and Gen Prayut's.
The new army chief commanded the 1st Army in charge of Bangkok and the central provinces before being promoted to assistant army chief. The 1st Army played a key role in the coup last year led by Gen Prayut, the then army chief.
The new navy commander will be Adm Na Areenij, who will be promoted from his present position of chief-of-staff, edging out assistant navy chief Adm Narongpol Na Bangchang, who was promoted to deputy navy chief in the reshuffle.
Adm Na won the nod reportedly because the defence minister wanted to maintain the tradition of reserving the top navy post for graduates of the Naval Academy. Adm Narongpol, who is a submarine expert, studied at the German naval academy.
A navy source said Adm Narongpol may now resign from the service.