The Harvard-educated Pita, 43, whose bid to become premier last year was thwarted by lawmakers allied with the royalist military, was cleared of wrongdoing as the Constitutional Court deemed the firm he held shares in had no broadcast concession and was not a mass media organisation.
"I will continue to work for the people ... and give it my all as the opposition," Pita said as he emerged from the court smiling at cheering supporters.
The verdict will be a boost for his anti-establishment Move Forward Party, the surprise winner of the 2023 election, after it courted young and urban voters with a bold agenda to end business monopolies and change a law that punishes insults of the monarchy with long prison terms.
As the biggest party in parliament, Move Forward remains a long-term threat to the status quo, maintaining appeal among liberal voters through its charismatic politicians and creative use of social media.
It is not out of the woods yet, however, with the same court due to decide next week on whether its push to amend the law on royal insults is unconstitutional and tantamount to an attempt to "overthrow the democratic regime of government with the king as the head of state".
BATTLE FOR POWER
The cases are part of a two-decade battle for power in Thailand that broadly pits royalists, military and old money families against parties elected on populist or progressive platforms.
Move Forward's efforts to form a government were repeatedly stymied by senators appointed by a junta, amid conservative outrage over its plan to amend the law insulating the powerful monarchy from criticism.
Move Forward's supporters fear an unfavorable ruling next week could lead to more serious legal moves against the party that could result in its dissolution and political bans for its executives.
Its predecessor, Future Forward, was disbanded for violating campaign funding rules and its former leader and prime minister candidate Thanathorn Juangroongruangkit was disqualified over a shareholding issue.
The court cleared Pita to return to parliament from suspension. Asked if that would be as Move Forward leader, he said "nothing at this stage".
An opinion poll last month showed that despite his absence from politics, Pita remains popular, backed by 39% of respondents, with Prime Minister Srettha Thavisin at 22%.
"I'm so, so happy," supporter Napatsorn Boonlee, 61, said of Pita being cleared. "I want him to be PM. I voted him. I'm glad to see this."
