The commission announced Wednesday that Thanathorn Juangroongruangkit, leader of the now-defunct Future Forward Party, had knowingly violated the law when he ran for office without divesting himself of a mass media company by a legal deadline.
The Constitutional Court has already found him guilty of violating the law and barred him from taking the parliamentary seat he had won. But the court did not rule on whether Thanathorn had intentionally broken the law.
Thanathorn has argued that he met the deadline.
If found guilty of intentionally violating the law, he could face a prison term of one to 10 years, a fine and a ban from political office for 20 years.
Many of the former party's supporters believe it was targeted for dissolution because of its outspoken anti-establishment positions that have been an irritant to the government and the conservative forces in Thai society.
It had been critical of the military for its interference in politics and sought to amend the constitution, drafted under military rule, to make it more democratic.
The court also imposed a 10-year ban on the party's executive members holding political office.
Eleven executive members of the party who had been serving as lawmakers were forced to give up their seats. The party's remaining 65 MPs could keep their positions by becoming members of another party within 60 days.
Several of the party's lawmakers crossed over to become members of rival parties, but a bloc of 55 have agreed to join together in the Move Forward Party, which vows to share the positions of Future Forward.