Rukchanok Srinork arrived on Wednesday at the court building in the capital, Bangkok, while her fellow lawmakers were convening in parliament.
"I submitted a request to postpone (the hearing) because today the new parliament convenes for its first session, but the court refused. So I came to hear the verdict," she told reporters, standing next to her party leader who was there to lend support.
She was charged over two posts she allegedly shared two years ago on X: a post that reportedly defamed the monarchy over links to a coronavirus vaccine and a repost of an anti-monarchy quote by 18th-century French philosopher Denis Diderot.
Srinork was sentenced to three years on each count under Article 112 of Thailand's Criminal Code which protects the monarchy, known as lese majeste. She was also convicted under the Computer Crime Act, whose broad provisions covering online activities have been criticised as a threat to freedom of expression.
She has appealed the sentence and applied for bail. If denied, she will lose her lawmaker status.
The parliamentarian had denied she posted the tweets, calling the case against her "weak". The plaintiff reportedly provided screenshots of the posts, but the police couldn't find the links.
Srinork, 29, won a seat in May's general election, part of a shock victory for the progressive Move Forward Party that shook Thai politics. The win did not translate into power due to the party being ultimately out-manoeuvred by powerful conservative forces. She was initially a defender of the conservative establishment before switching sides and joining the progressive movement.
The monarchy and the laws that protect it have come under pressure in the last few years. In 2020, tens of thousands - predominantly young people - marched in several Thai cities, demanding constitutional reform and the abolition of the commonly named "112 law". The government's response was an unprecedented slew of prosecutions.
In 2021, pro-democracy activists launched a campaign calling for repealing the law.
Critics say the lese majeste law is often used to quash political dissent. The law makes insulting the monarch, his immediate family and the regent punishable by up to 15 years in prison.
