Sondhi Limthongkul, the media baron who spearheaded street demonstrations which culminated in the coup against Thaksin, was released on 300,000 baht (S$14,490) bail pending an appeal, the Criminal Court in Bangkok said on Tuesday.
He was convicted over claims made at a rally in Bangkok in March last year.
Sondhi had said that Thaksin had tried to have him assassinated.
The media baron had also accused the government of burning down a stage used by the protesters on the resort island of Phuket, and said Thaksin was overly superstitious.
Sondhi had already been convicted in March this year of defaming a minister in Thaksin's government. That case is also on appeal.
He has been largely silent since the military ousted Thaksin in September last year.