Mongkol Thirakot, 30, was first given a 28-year sentence for remarks he made on Facebook three years prior.
However, an appeals court increased the sentence by an additional 22 years on Thursday.
The law known as lese majeste makes disparaging remarks about the monarchy illegal.
The law, which has drawn a lot of criticism, is still in effect even after a civilian government was elected for the first time in ten years last year.
Thirakot, 30, was first sentenced to 28 years for comments he had made on Facebook three years earlier.
On Thursday, though, an appeals court raised the sentence by an extra 22 years.
Insults against the monarchy are forbidden by the lese majeste law.
Much criticism has been directed at the law, which remains in force despite last year’s election of a civilian government for the first time in ten years.
The judge stated during the hearing on Thursday that Mr. Thirakot’s cooperative behavior had already resulted in a sentence reduction of one-third.
The reasons behind the severe punishment meted out to Mr. Thirakot, an internet clothes seller from the province of Chiang Rai, have not been made public. The judge brought up several Facebook comments, and it is common for Thai courts to impose extra punishments for every post.
At the beginning of King Vajiralongkorn’s reign in 2019, the lese majeste law was temporarily suspended. However, since the start of extraordinary student-led protests three years prior, demanding broad changes to the monarchy, the law has been reinstated and widely utilized.
Arnon Nampa, an activist and attorney who was the first to advocate for a public conversation about monarchy, also had his sentence to prison extended by four years on Wednesday.
The Constitutional Court will make a decision later in January regarding Move Forward’s dissolution. Move Forward is a young party that won the most votes in the previous year’s general election. Move Forward has called for amending the lese majeste law, which some Thai conservatives believe is an attempt to topple the entire political system.