The formal opening of the new parliament is expected within 15 days after the Election Commission (EC) on Monday endorsed all 500 MPs elected at the May 14 general election.
Under Section 121 of the constitution, the first parliament meeting must be convened within 15 days from the day the EC endorses at least 95% of all MPs-elect.
A source said the selection of the new House speaker and his two deputies is expected to take place on the first day of the new parliamentary session, but the parliamentary selection of Thailand's next prime minister will take place only after the selection of the House speaker gets royal endorsement.
The selection of the House speaker will be scheduled after the state opening of parliament, which marks the formal start of the new parliamentary year, said the same source.
The 500 MPs-elect endorsed by the EC on Monday are from 67 parties -- 400 MPs elected in the constituency system and 100 in the party-list system.
The endorsement contradicted previous media reports, which said 71 MPs-elect in 37 constituencies might be suspended over election fraud complaints.
EC secretary-general Sawang Boonmee, meanwhile, said the EC resolved to endorse all MPs-elect because it came to the conclusion that it won't be able to ensure fairness for all sides if it has to rush its investigation into complaints lodged against the results of the election and wrap it up within the given 60-day time frame.
Under Section 138 of the 2018 organic law on the election of MPs, the EC still has the authority to continue investigating these complaints for up to a year after receiving them, according to Mr Sawang.
And if the EC has sufficient evidence to believe an MP had committed or been involved in an election fraud as accused, the EC can still petition the Supreme Court to retrospectively forfeit their right to contest an election and vote in one, he said.
All MPs who stand accused of election fraud will be allowed sufficient time to defend themselves against the allegations to ensure justice for them, too, he said.
When asked if the EC will next seek the Constitutional Court's interpretation of Move Forward Party (MFP) leader Pita Limjaroenrat's alleged ineligibility to contest the election after also endorsing his MP status, Mr Sawang said the EC's fact-finding committee is still investigating the case.
The EC is being pressured by several senators to call on the court to rule whether Mr Pita's past holding of 42,000 shares in iTV Plc made him ineligible to contest the election from the beginning.
Mr Pita has insisted he only served as executor of his late father's estate, of which the shares were a part.
The MFP leader reportedly transferred the shares last month.
Mr Sawang said the EC would not mix its responsibility to investigate claims against Mr Pita with politics; hence whether or not the investigation will be concluded in time before the selection of the country's new prime minister takes place isn't something that concerns the EC.
"In the way we work, all facts deemed necessary for the ongoing investigation must be completely extracted first … and even if the process has to be expedited later, it will still have nothing to do with politics," he said.
Mr Pita is the sole prime ministerial candidate of the MFP and is expected to become the next prime minister.
All MPs who have been endorsed by the EC will be able to pick up their letter of endorsement from the EC from today until Saturday.
The document must be shown to the Secretariat of the House of Representatives upon reporting for the first time as a new MP, said Mr Sawang.
Pornpith Phetchareon, secretary-general of the House of Representatives, said new MPs may report to the House from today onwards.
Pheu Thai Party secretary-general Prasert Chantararuangthong said he now expects to see the formation of the new coalition and the selection of the new prime minister to happen sooner than previously thought.
Considering the EC timeline for endorsing the election results, he said he personally believes Thailand's new prime minister will be officially named before the end of next month.