Former Thai Prime Minister Yingluck Shinawatra has been found guilty of criminal negligence and sentenced in absentia to five years in prison.
The Supreme Court convicted her of mishandling a rice subsidy scheme which allegedly cost Thailand at least $8bn.
Ousted in 2014, weeks before a military coup, and later impeached, Ms Yingluck denies all charges and fled before the verdict, reportedly to Dubai.
Public opinion is divided. She remains popular with rural and poor voters.
The Supreme Court judges said Ms Yingluck had been aware of the falsified rice deals but did nothing to stop it.
"The accused knew that the government-to-government rice contract was unlawful but did not prevent it," the court said in a statement.
"Which is a manner of seeking unlawful gains. Therefore, the action of the accused is considered negligence of duty," it said.
During her trial, Ms Yingluck had argued she was not responsible for the day-to-day running of the scheme and insisted she was a victim of political persecution.
Image copyright AFP The BBC's Jonathan Head in Bangkok says "the verdict sets an awkward precedent, criminalising a prime minister for a policy, which was a central part of her election manifesto".
"There has been no suggestion that she was herself involved in any corruption," he explains.
What was the rice scheme?
- Part of Ms Yingluck's election campaign, it was launched after she took office in 2011.
- To alleviate rural poverty, the government paid rural farmers nearly twice the market rate.
- The scheme hit Thailand's rice exports, leading to an estimated loss the military government says was at least $8bn.
Though popular with her rural voter base, the scheme was too expensive and open to corruption, her opponents said.
Where is she now?
Ms Yingluck is thought to be in Dubai where her brother, former Prime Minister Thaksin Shinawatra, lives in self-imposed exile avoiding a 2008 sentence for corruption.
Ms Yingluck entered politics only after his sentence and was seen by critics as a proxy for her ousted brother.
Both siblings remain popular among Thailand's rural poor, but are opposed by an urban and middle-class elite.
She is unlikely to serve any of her sentence because she is out of the country.
The trail ran over two years, with a ruling initially scheduled for late August. When Ms Yingluck surprisingly failed to show up in court, the verdict was postponed and an arrest warrant was issued for her.
Timeline of the controversy
May 2011- Yingluck Shinawatra is elected PM, and shortly afterwards begins rolling out her rice subsidy scheme
January 2014 - Thailand's anti-corruption authorities investigate Ms Yingluck in connection to the scheme
May 2014 - She is forced to step down from her post after Thailand's constitutional court finds her guilty of abuse of power in another case. Weeks later the military ousts what remains of her government
January 2015 - An army-backed legislature impeaches Ms Yingluck for corruption over her role in the rice scheme, which effectively bans her from politics for five years. It also launches legal proceedings against her
August 2017 - Ms Yingluck fails to appear at court for the verdict, claiming ill health. It is later thought she left for Dubai.