The Election Commission (EC) has chosen one of its members, Ittiporn Boonpracong, as the group's new chairman and the Constitution Drafting Committee (CDC) chairman said the selection was legal.
A meeting of five newly endorsed EC members on Tuesday picked Mr Ittiporn, a former ambassador to the Netherlands, from among their own ranks to head the body.
The next step will be for the secretary-general of the National Legislative Assembly (NLA) to notify NLA president Pornpetch Wichitcholchai so he can submit the names of the new chairman and the four election commissioners for royal endorsement.
Last Thursday, law lecturer Jade Donavanik, adviser to the CDC, warned that picking a chairman from among the existing EC members could be in breach of the law.
He said the law states that the first chairman to be named since it was enacted can only be chosen after all seven election commissioners have been installed.
But two seats remain empty as the NLA voted on July 12 to endorse five nominees for the commission and rejected two candidates.
Mr Jade said the two commissioners who have yet to be picked also have the right to choose a chairman and it would be unfair to strip them of this by allowing the selection meeting to go ahead in their absence.
But CDC chairman Meechai Ruchupan on Tuesday insisted a new law governing the poll organising agency allows the five new commissioners to select a chairman.
Mr Meechai said he discussed the matter with Mr Jade. Mr Jade told him five was okay but seven would have been better.
"The law clearly states that an EC chairman can be chosen when five election commissioners have been installed. If there was no hurry, we could have waited until the last two seats were filled," Mr Meechai said.
"But the country needs to move forward as an election will be held in the near future. We can't wait until all seven have been selected."
A spokesman for the NLA whip, Jate Siratharanont, said the selection of the new EC chairman could not be avoided because that person would be playing a key role in supervising the election that has been tentatively set for February.
Mr Jade expressed confidence that the selection of the chairman would not face any legal complaints because the CDC, which drew up the law governing the poll organising agency, had confirmed the selection was in compliance with the constitution and the law.