The Appeal Court has upheld a lower court's ruling that sentenced former Palang Pracharath Party (PPRP) MP Pareena Kraikupt to eight months in jail, suspended for two years.
The lower court's sentencing was for a defamation suit filed against Ms Pareena by Progressive Movement spokeswoman Pannika Wanich.
The sentencing also includes a fine of 66,666 baht.
Ms Pareena arrived at the court on Tuesday to hear the ruling.
In the suit, Ms Pannika, then-spokeswoman of the Future Forward Party (FFP), accused Ms Pareena, then a Palang Pracharath MP for Ratchaburi, of posting a defamatory message on Facebook on Aug 4, 2019.
The message implied that Ms Pannika and then-FFP leader Thanathorn Juangroongruangkit were linked to a series of bombings in Bangkok and the three southernmost provinces of Yala, Pattani and Narathiwat in August 2019.
Ms Pareena's Facebook post was false and caused damage to the plaintiff, it was declared in Ms Pannika's suit.
The Criminal Court first sentenced Ms Pareena to one year in jail and a fine of 100,000 baht. The court later commuted the sentence to eight months in jail and a fine of 66,666 baht as the defendant gave a useful statement. As she had never been jailed before, the court suspended her prison term for two years but she still appealed.
Ms Pareena lost her seat as a government MP after the Supreme Court in April disqualified her from politics for life over her illegal use of land in a forest reserve in her home province of Ratchaburi.