National Legislative Assembly (NLA) president Pornpetch Wichitcholchai is first in line to assume of the role of Senate Speaker, according to a government source.
Mr Pornpetch has reportedly tendered his resignation as a member of the Council of State in preparation to become one of 250 senators appointed by the National Council for Peace and Order (NCPO).
Several members of the Council of State are expected to quit their job and join the Senate out of concern about conflicts of interest. The Senate screens draft bills while the Council of State is the government's legal adviser.
The regime is expected to submit a list of names for royal endorsement on Friday after the MPs are officially certified by the Election Commission (EC).
Speculation about the Senate, whose first key task will be to join the House of Representatives in choosing a new prime minister, is growing and it is understood that several cabinet ministers, NLA members and former members of the coup-sponsored reform councils will be picked.
Among them are Deputy Prime Minister Gen Chatchai Sarikulya, Deputy PM and Justice Minister ACM Prajin Juntong, Labour Minister Pol Gen Adul Sangsingkeo, and Education Minister Teerakiat Jareonsettasin. They are expected to resign from the cabinet prior to the appointment.
Based on the latest report, Foreign Minister Don Pramudwinai is expected to join the Senate but it unclear if or when he would resign as he is scheduled to join the Asean Summit from June 22-23.
Somchai Saweangkarn is among the NLA members widely speculated to become senators; others include Surachai Liangboonlertchai, Pirasak Porjit and Wanlop Tangkhananurak.