Future Forward Party leader Thanathorn Juangroongruangkit on Saturday denied three counts of sedition when he reported to police at Pathumwan police station.
Police charged him with violating Article 116 of the Criminal Cod by inciting unrest, violating Article 189 of the Criminal Code by helping a student activist flee from an arrest and violating Article 215 by taking part in an unlawful gathering to cause disturbance in the country.
As he left the police station, he said he denied all the charges.
He said he reserved his right not to give a verbal account to police but he would submit his written account before May 15.
Thanathorn said he was confident in his innocence but he was worried that he would be tried in a military court instead of the Criminal Court.
He said representatives of foreign embassies came to observe the situation because they want to know from police why the case would go to a military court.
The embassies' representatives also asked police why Thanathorn was summoned now, although the case dated back to 2015.
Police said the case was delayed because officers in charge had retired and the case had to be handed over to new officers.
Before leaving, Thanathorn asked his supporters to disperse peacefully so that people with malicious intention could not use the chance to create a situation.
He said he would keep his supporters updated on his case via Facebook.
He then raised a three-finger sign to the supporters who flashed back a three-finger sign as Thanathorn left the scene.