Patee Sarasin stepped down as chief executive of Nok Air on 14 September, and has been succeeded by NokScoot chief Piya Yodmani.
Sarasin, who has led the carrier since its establishment in 2004, will remain on Nok's board and has been appointed as vice-chairman. It is unclear if he will remain as chairman of NokScoot.
In recent months, local media reports said that major shareholder Thai Airways International was unhappy with Sarasin's management of the loss-making budget carrier, and had been seeking to remove him.
The flag carrier also declined to participate in Nok's fund raising exercise in May, which saw its shareholding dilute to 21.6%.