Mohamed Reda Taoujini was arrested and sentenced to two years in prison and a fine of 20,000 Moroccan dirhams (around $1,850) in February in the southwestern city of Agadir after Justice Minister Abdellatif Ouahbi filed two complaints against him.
Tuesday's sentence came in an appeal ruling, extending Taoujini's jail time to four years, his lawyer Redouane Arabi told AFP, denouncing the ruling as "very severe."
Taoujini, who has more than 490,000 subscribers on YouTube, was accused of defaming Ouahbi in two videos he released on the platform.
In the videos, he questioned whether the minister had been involved in a drug trafficking scandal that has become known in Morocco as the "Escobar of the Sahara" affair.
The case came to light after the arrest late last year of two elected officials from the minister's Authenticity and Modernity Party (PAM) as part of an investigation into a large drug trafficking ring.
The investigation identified 25 people suspected of "possession, marketing and export of drugs," as well as corruption, prosecutors say.
Twenty of them have been detained so far.
The suspects are believed to be linked to Hadj Ahmed Ben Brahim, a Malian serving a 10-year sentence in Morocco for international drug trafficking.
Nicknamed the "Pablo Escobar of the Sahara," Ben Brahim was arrested in 2019 in Casablanca after the record seizure of 40 tons of hashish in 2015 in trucks belonging to him.