Hundreds of supporters gathered at Pathumwan police station on Saturday morning as Future Forward Party leader Thanathorn Juangroongruangkit reported to face sedition charges.
Four companies of 620 policemen were deployed to control the crowd and barriers were placed at the police station.
When Thanathorn arrived at 10am he used a megaphone to thank his supporters, who had been waiting for him to show up since early morning.
The supporters shouted "Thanathorn fight on" and many carried signs that read "#Save Thanathorn".
As well as the supporters, 12 representatives from 10 countries, including UK, Finland, US, France, Netherland and Canada, were at the scene to observe the situation.
Thanathorn asked his supporters to stay calm and not push inside the police station.
While Thanathorn he walked into the police station, representatives of the foreign embassies shook his hands in a show of support.
Thanathorn also turned to his supporters and flashed a three-finger sign, a sign of rebellion against dictatorship from the Hunger Games, to the cheers of his supporters.
Thanathorn is accused of violating Article 116 of Criminal Code with an action deemed detrimental to national security.
The accusation reportedly dates back to an incident in 2015, when anti-junta student activists resisted detention by the authority. Thanathorn is accused of providing a vehicle for students to flee.