Jatuporn was taken to the Bangkok Remand Prison immediately after the verdict was announced.
The court, however, upheld the release on bail of four other key figures.
The ruling against Jatuporn, chairman of the United Front for Democracy against Dictatorship (UDD), followed a prosecutor’s request that bail for the five red-shirt leaders including Jatuporn be revoked in relation to terrorism charges filed against them in relation to the street protests in 2010.
According to the petition, the five were accused of breaching their bail conditions, which banned provocative activity that could hurt the public’s feelings or damage a third party’s reputation.
The prosecutor presented the court with recordings of TV programmes featuring Jatuporn, which the court found provocative and defamatory.
The other red-shirt leaders said they accepted the verdict but would seek Jatuporn’s release.
“We will not appoint anyone to replace Jatuporn. Instead we will fight and wait until he returns,” key UDD figure Nattawut Saikua said.
The court did not revoke the bail for Nattawut, Weng Tojirakarn, Veerakarn Musikapong and Nisit Sinthupai, finding their public statements to be just expressions of opinion.
Before the ruling, Jatuporn defended himself by saying he had only voiced his opinion in line with his right to free expression. However, he accepted other facts presented in the case, including that he had appeared on TV programmes and given interviews.
“My speeches over the past two years did nothing to incite agitation. And if someone was defamed then they should have filed a petition against me,” he said.
Jatuporn added that he was prepared for the ruling because he had been jailed twice before. Upon arriving in court, the red-shirt leader showed a backpack containing clothes and other items.
When red-shirts, in the court room began to cry in response to the verdict, Nattawut urged them not to panic, saying he still believed in the judicial process. He called on the state to treat Jatuporn fairly.