A 61-year-old man was jailed for 18 years on Wednesday for posting six video clips deemed insulting to the monarchy, his lawyer said.
Tara, whose last name was withheld by his lawyer, was arrested in 2015 for sharing online materials allegedly insulting to the monarchy.
He was charged with royal defamation and computer crime.
The Bangkok military court sentenced Tara to 18 years in jail for violating Article 112 of the criminal code, Yaowalak Anuphan, head of the Thai Lawyers for Human Rights Centre, told Reuters.
"He accepted the charge against him and has been in custody since 2015 so the court sentenced him to 20 years in prison, minus two years," she said.
Tara cannot appeal his sentence, Ms Yaowalak said, because he was arrested while Thailand was under martial law.