Ms Yingluck entered politics only after his sentence and was seen by critics as a proxy for her ousted brother. Nothing has been heard from Yingluck since she fled the country, and one of her lawyers, Sommai Koosap, told Reuters outside the court on Wednesday that she has not been in contact.
Yingluck became prime minister in 2011. The court then seized her 30-million baht bail and issued her arrest warrant.
The charges she was faced with pertained to mishandling a subsidy scheme for rice which is reported to have cost Thailand at least £8bn.
"The accused knew that the government-to-government rice contract was unlawful but did not prevent it", the court said in a statement.
The court said that although Shinawatra herself did not profit from it, she did not stop the corruption happening under her watch. "I have spies", he said, adding that to his knowledge Ms Yingluck has not sought asylum overseas.
Her negligence incurred up to 500 billion baht loss to the state and also damaged the country's rice trading market.
While there was no suspension of the term, Yingluck was not hit with the maximum sentence of 10 years and a 20,000 baht ($601) fine.
The trail ran over two years, with a ruling initially scheduled for late August.