A court determined the comments posted on Hamad al-Naqi's Twitter account, which also insulted the kings of Saudi Arabia and Bahrain, endangered national security.
He was sentenced to a decade behind bars in June 2012 and the Kuwaiti Court of Appeals upheld the sentence Monday.
Human Rights Watch issued a statement Tuesday condemning the court's decision, saying the attempt to criminalize peaceful criticism violates international standards on freedom of expression.
"Ten years in prison for peaceful criticism shows just how little Kuwait respects freedom of expression," said Joe Stork, deputy Middle East director. "Locking up critics isn't going to make Kuwait's political crisis go away."
Human Rights Watch called on Kuwaiti authorities to drop charges against those accused or convicted of crimes based on freedom of expression.