According to the legal watchdog Thai Lawyers for Human Rights, Prapanukul, 57, provided legal assistance to members of a political opposition group, the United Front for Democracy Against Dictatorship.
He also served as legal counsel in a high-profile royal insult case.
He was detained in a raid on his home by police and troops on the weekend.
Prawet appeared in a Bangkok court on Wednesday and was charged with 10 counts of royal insult and three counts of breaking Section 116 of Thailand’s criminal code, the equivalent of sedition.
“Prawet faces 10 counts of breaking Article 112, so that works out to up to 150 years in prison if he is found guilty,” Anon Nampha of Thai Lawyers for Human Rights told Reuters.
“He also faces three separate charges of breaking Article 116 which carries a maximum sentence of seven years in prison for each offence.”
It was not immediately clear what Prawet had written or said that led to his arrest and charges.
