Bangkok’s Military Court found Pongsak Sriboonpeng, 48, guilty of posting messages and pictures defaming the monarchy in six posts on the social networking website.
He was sentenced to 10 years on each count with the 60-year jail term halved after he pleaded guilty, his lawyer Sasinan Thamnithinan said.
“It’s broken the record,” she said about the severe jail term, adding that because Pongsak was arrested while Thailand was still under martial law there was no right to appeal the sentence passed by the military court.
Lese majeste convictions have surged since the military seized power in May 2014.
According to iLaw, a local rights group that monitors such cases, there were just two ongoing prosecutions for royal defamation before the coup. Now that number is at least 56.
Critics of the law say it is being used as a weapon against political enemies of the royalist elite and their military allies and now targets those opposed to the coup.
In another conviction this week a military court in Chiang Rai province sentenced a man with a history of mental illness to five years in jail for lese majeste.
Samak Pantay, 48, was found guilty on Thursday of damaging a portrait of the King and Queen in July last year, lawyer Anon Numpa said.
“He confessed to the charge so the judge commuted the sentence to five years,” he said, adding that Samak has been medically certified as mentally sick for “more than 10 years”.