In the first meeting of the NLA on Aug 7 Mr Pornpetch was elected NLA president and Surachai Liengboonlertchai and Phirasak Porjit first and second deputy presidents respectively.
Mr Pornpetch said on Sunday morning he had been informed that a royal command to formally appoint him and his two deputies would be issued today.
He said the Office of the Senate Secretariat had prepared to hold a ceremony for him to receive the royal command on Monday at 9.09am.
If all went as expected, the NLA would be able to hold its second meeting on Monday as well.
Mr Pornpetch said he had earlier asked NLA members to be prepared to deliberate the draft 2015 Budget Bill from the second meeting.