National Security Council deputy secretary-general Pongsakorn Rodchompoo has been transferred to an inactive post in what is seen as a move to clear the agency of the influence of deposed prime minister Thaksin Shinawatra.
Prime Minister Prayut Chan-o-cha exercised his power under Section 44 of the interim charter on Tuesday, to create a new position of adviser in the Prime Minister's Office for Lt Gen Pongsakorn.
The transfer order took effect yesterday, when it was published in the Royal Gazette.
The position of prime minister's adviser is widely known as an inactive post for civil servants.
Pakorn Srichan-ngam, assistant to the NSC secretary-general, was promoted to deputy secretary-general under the same order.
An NSC source said the transfer is part of a campaign to stamp out the influence of officials who are sympathetic to Thaksin and his associates.
The source said Lt Gen Pongsakorn was appointed to the NSC by then-prime minister Yingluck Shinawatra, moving from the Supreme Command, two years ago.
The source said the removal of Lt Gen Pongsakorn opens the way for Kanokthip Rajatanun, another NSC deputy secretary-general, to be promoted to lead the security agency.
With the departure of Lt Gen Pongsakorn, Ms Kanokthip now is the most senior NSC deputy chief, a status that makes her eligible to succeed NSC chief Anusit Kunakorn, who will retire on Sept 30.
She is now tipped to become the first woman to head the NSC.