The appointment of Sonthi, ex-army chief and ex-chairman of the Council for National Security, was sent for announcement in the Royal Gazette at 3:30 pm.
Sonthi retired as army chief at the end of September and resigned as CNS chairman on Monday.
His appointment followed the resignations of five Cabinet members, who were found to have violated the 5-per cent share holding limit.
Prime Minister Surayud Chulanont said Sonthi's appointment was submitted for the royal command on September 30.
He said another list of Cabinet reshuffle would be submitted for a royal command Tuesday evening.'
Surayud indicated that he would concurrently hold the post of interior minister by saying that he would supervise the election by himself.
Surayud said he expects that the second reshuffle list would be approved by a royal command on Wednesday.