An Australian writer has been sentenced to three years in a Thai jail after pleading guilty to lese-majeste charges for insulting the country’s King.

Harry Nicolaides, a 41-year-old Greek-Australian, pleaded guilty to defaming Thailand’s revered royal family in his self-published 2005 novel Verisimilitude.

"I plead guilty," Nicolaides told a Thai judge on Monday, after charges of slandering the 81-year-old King Bhumibol Adulyadej and other members of the royal family, including the crown prince, were read out to him in court.

Nicolaides has already spent four months in jail after being arrested at Bangkok airport in August.

"He was found guilty under criminal law article 112 and the court has sentenced him to six years, but due to his confession, which is beneficial to the case, the sentence is reduced to three years," a judge told the court.

Dressed in an orange prison jumpsuit and shackled at the ankles, Nicolaides earlier choked back tears as he described his jail time as like being in Alice in Wonderland.

"This is an Alice in Wonderland experience. I really believe that I am going to wake up and all of you will be gone," Nicolaides told reporters.

“I would like to apologize. This can't be real. It feels like a bad dream.

"I respect the king of Thailand," he added. "I was aware there were obscure laws (about the monarchy) but I didn't think they would apply to me."

During his time in jail he said he had endured “unspeakable suffering”, but would not elaborate.

Nicolaides is a frequent visitor to Thailand, where he worked as a university lecturer and resided from 2003-2005.

He has described his novel as a commentary on political and social life of contemporary Thailand. A Thai website described the book as an "uncompromising assault on the patrician values of the monarchy". It has been reported only seven copies of the book have been sold.

Lese-majeste, or insulting the monarchy, is regarded as a serious offence in Thailand, punishable by up to 15 years in prison.

In 2007 a Swiss man, Oliver Jufer, was sentenced to 10 years in jail for defacing pictures of the king but he was later given a royal pardon and deported from the country.

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