A Bangkok military court convicted the 34-year-old of ten counts of lese majeste for posting photos and videos of the royal family on a Facebook account that purported to belong to a different user.
Wichai, whose last name was withheld to protect his relatives from ostracisation, was accused of using the account to slander a former friend, said iLaw, a group that tracks royal defamation cases.
"The court punished him with seven years per count. Altogether he was given 70 years, but it was reduced in half because he confessed," said Yingcheep Atchanont from iLaw.
Reporters were barred from entering the military court where Wichai's verdict was read.
Later on Friday a criminal court sentenced another lese majeste suspect to 2.5 years in jail for uploading an audio clip from an underground political radio show that was deemed insulting to the monarchy.
More than 100 people have been charged under lese majeste law since the coup.
According to iLaw, Wichai initially denied the charges but later confessed after waiting for more than a year in jail for the court proceedings to begin.