The Criminal Court on Tuesday found Pheu Thai spokesman Prompong Nopparit and co-defendant Kiatudom Menasahwat guilty of libel and handed down one-year jail terms suspended for two years as it was a first offence.
Reading the verdict, the court reprimanded the pair for omitting to verify the information before holding a press conference to attack Constitution Court president Wasan Soypisudh on June 3, 2010.
The court said the pair had maliciously and falsely portrayed Wasan for lacking impartiality.
In addition to the suspended imprisonment, the pair will have to pay a fine of Bt50,000 and publish the summary verdict in three newspapers for seven days.
Reacting to his conviction, Prompong said he respected the judicial decision but he would seek an appellate review in a bid to overturn the ruling.