The parliament will convene in joint session to vote for a new prime minister at 9.30am on Thursday next week, House Speaker Wan Muhamad Noor Matha said on Wednesday.
Mr Wan, ex-officio president of the parliament, said he set the date in consultation with Senate Speaker Pornpetch Wichitcholchai.
The 250 appointed senators are entitled by the constitution to participate in the vote, along with the 500 elected members of the House of Representatives.
Mr Wan said voting on July 13 for the new prime minister may be completed immediately, or not. The new prime minister needs the support of 376 votes of the joint sitting. If there is no definitive outcome, another voting session will be scheduled.
"The parliament must convene until the prime minister is installed. Mr Pita is not the only candidate," Mr Wan said, referring to Pita Limjaroenrat, the leader of the coalition-leading Move Forward Party (MFP).
"Mr Pita may be endorsed. ... Otherwise, a new prime minister must be picked anyway. Under the constitution, the parliament is duty-bound to elect a prime minister of the national administration. The country cannot lack a prime minister," the House speaker said.
Mr Pita's MFP won the most seats in the May 14 general election and has the first right to attempt to form a government.
Based on Tuesday's votes for MFP MP Padipat Suntiphada, who was elected first deputy speaker, Mr Wan said, the eight coalition parties were able to muster 312 votes of support for Mr Pita as prime minister next week. They need 64 more votes to reach the required minimum support of 376.
If Mr Pita was not voted in as prime minister in the first round, the constitution did not stipulate if a previously nominated person or a new candidate should be presented to the joint sitting.
However, candidates must be from among those previously verified by the Election Commission and their names listed as prime ministerial candidates of political parties.
If all those registered fail to win endorsement from the House and the Senate, an outside candidate can be nominated, but must win at least two-thirds of the votes at a joint sitting, Mr Wan said.
"If the joint sitting is unable to decide on the next prime minister at its first meeting, the next session for a vote will depend on suitability and the opinions of relevant parties.
"The keys are suitability and readiness, especially the attendance of members (of the parliament). Unless the members are ready to attend there will be a lack of a quorum," Mr Wan said.
MFP leader Pita is the favoured prime ministerial candidate of the eight coalition allies but is up against complaints questioning his eligibility for political office, mainly in relation to a shareholding in iTV Plc, part of his late father's managed estate. The constitution bans a shareholder of a media company from standing in a general election.
