Pita Limjaroenrat has resigned as leader of the Move Forward Party (MFP) to make way for his successor to take up the post of opposition leader.
Mr Pita, who has been included on the TIME100 Next list of young global leaders to watch, shared his resignation message on his Facebook page on Friday, addressing it to all MFP members and the general public.
In his message, Mr Pita said that while the MFP has the largest number of MPs within the opposition bloc, he cannot accept the position of opposition leader due to his suspension by the Constitutional Court from performing his duties as an MP.
"I have decided to step down from my position as the MFP leader, allowing the party to select an MP capable of assuming the role of 'opposition leader' to replace me as party leader."
The 43-year-old alumnus of Harvard Kennedy School of Government said that despite his resignation, he would still work for the MFP and the people to the best of his ability.
Observers have speculated that Chaithawat Tulathon, the party secretary-general, is the likely successor to Mr Pita.