The woman, Chayapa Shokpornbudsri, was found guilty Tuesday of defaming the monarchy on Facebook at a hearing held without her lawyer's presence, a court official told AFP.
The 49-year-old was handed a 19-year sentence which was cut to nine and a half years after she pleaded guilty, the official said, adding it was "a secret ruling".
"From her Facebook posts, she was found guilty of defaming the monarchy, threatening state security and violations of the computer crimes act," the court official said on condition of anonymity.
Chayapa's lawyer Khumklao Songsomboon, from Thai Lawyers for Human Rights, told AFP Wednesday she had not been informed of the court hearing in advance.
Chayapa "was crying when she rang yesterday... I only knew about the verdict after it had happened," Khumklao said.
"I don't know why [they didn't tell me]. I don't know what the court's intention was," she said, adding the lack of notice violated her client's human rights.
Chayapa "was accused of posting some messages in June about a counter-coup that could have created chaos in the country and which defamed the monarchy," she added.
AFP