He tipped as a favourite to replace Deputy Prime Minister Somkid Jatusripitak.

Thosaporn said he was still doing his job as the secretary general of the National Economic and Social Development Council (NESDC) and was supervising project spending under a 400 billion baht ($12.63 billion) borrowing plan.

"However, after my retirement, I'm very happy to support the work of the prime minister behind the scenes," he said in a statement.

(Reporting by Orathai Sriring; Editing by Martin Petty)