A leader of Thailand's "red shirt" opposition group was jailed for two years on Tuesday for insulting the monarchy during a street protest in 2010.
The Supreme Court said it had upheld the ruling of a lower court that Yosvaris Chuklom, also a comedian, was guilty of the crime of lese majeste, which can carry a penalty of up to 15 years for each offense.
The military government has made increasing use of the royal insult law against critics since taking power in 2014.
Yosvaris was a leader of the group loyal to the populist movement of ousted prime minister Thaksin Shinawatra and his sister, Yingluck Shinawatra, who was prime minister in the government that was overthrown in the last coup.
Although Yosvaris did not name the king in his speech in 2010, at a time the red shirts were in opposition, the court ruled that his gestures had made the insult clear. He had said he no intention of insulting the king.
Neither he nor his lawyer made any comment after the Supreme Court's ruling.
There has been a significant increase in the use of the lese majeste laws since the widely revered King Bhumibol Adulyadej died in October after seven decades on the throne. He was succeeded by his son, King Maha Vajiralongkon.