The lawsuit was filed by Mr Tankhun, who accused Mr Karun of making remarks construed as insulting him and damaging to his reputation at two campaign rallies in Don Muang district on June 3 and 12, 2011. The two were rival candidates in Bangkok's Constituency 12 in the July 3, 2011 election.
The court found Mr Karun guilty and sentenced him to two years in jail without suspension. The sentence was commuted one-third to one year and four months for his useful testimony during the trial.
Mr Karun said he would apply for bail, pending an appeal.