Abdessamad Haydour, 24, a student at a technical college, has served 18 months of a 3-year prison sentence for comments he made during a political debate that was taped by an onlooker and posted on Youtube. In the video, Haydour called Moroccan King Mohammed VI a "dog" and a "murderer" and a "dictator," Human Rights Watch said.
Morocco drafted a new constitution in 2011 that permits freedom of speech but the nation has yet to repeal a press law that makes derogatory comments about the king illegal.
Despite the new constitution lower courts have continued to enforce the press law and sentence people to prison terms for violating it.
Human Rights Watch said Haydour has served the longest prison term of anyone convicted in Morocco.
"If Morocco intends to carry out its new constitutional guarantees of free expression, it needs to get rid of laws that send people to jail for offending the head of state, even if what they say seems crude," said Joe Stork, acting Middle East and North Africa director at Human Rights Watch.