Arnuparb Tarntong resigned from the Move Forward Party on Friday after being accused of sexually harassing young women in his home.
The 38-year-old Bangkok city councillor said in a Facebook post that his resignation would take effect immediately to save the image of the party. He said he would concentrate on legal action against the people accusing him of misbehaviour.
He announced his decision after being summoned to appear before a Move Forward disciplinary committee, which decided to ask party executives to expel him.
Mr Arnuparb won a seat to represent Sathon district in the May 22 Bangkok council election, running under the Move Forward banner. He will continue to serve but without a party affiliation. He did not mention this issue in his message on the social networking platform.
Move Forward on Friday posted a message on its Facebook page demanding that he resign his councillor position to show political responsibility.
Mr Arnuparb was accused on Tuesday of sexually harassing women in complaints filed at the Thung Mahamek police station. It is unclear how many complaints have been filed but all of the complainants are said to be under 18 years old.
The complainants said the incidents took place on Monday when he invited four young women for drinks at his condominium unit after attending a party activity.
Mr Arnuparb said in another Facebook post on Thursday that he denied the charges and insisted on his innocence.
The latest allegations, coming not long after a series of sexual assault charges against former Democrat Party deputy leader Prinn Panitchpakdi, has led some civic groups to call for political parties to vet their members more carefully.