Mr Dinh has defended pro-democracy activists and bloggers
Four democracy activists have gone on trial in Vietnam, accused of plotting to overthrow the communist government.
Three of the defendants, including prominent human rights lawyer Le Cong Dinh, face charges that could potentially carry the death penalty.
They are said to have created anti-state documents and internet blogs.
The case has drawn strong criticism from rights groups abroad, who see it as a sign of an increasing clampdown on democracy and freedom of expression.
The hearing is scheduled to last two days.
Nga Pham, BBC Vietnamese Service
The arrests of these four dissidents have attracted huge attention, mainly because of the high profiles of the accused, especially Le Cong Dinh. He's a well-known figure in Vietnam, having represented the country in a number of international lawsuits.
Their indictment for subversion is rarely seen in Vietnam nowadays, and has sparked speculation that the government is tightening its grasp over political dissent in light of the upcoming Communist Party Congress.
Security is high outside the court, and state-controlled local media has written little about the trial.
It has been a long time since the communist regime tried anybody on subversion charges, considered one of the most serious offences under Vietnam's criminal code, says the BBC's Nga Pham.
The four accused - who were arrested in June - were initially charged with spreading anti-government propaganda.
But early last month, state prosecutors decided to bring more serious charges.
Le Cong Dinh and one of the other defendants, Nguyen Tien Trung, have admitted the charges brought by the prosecution, but a third defendant, Le Thang Long, has denied any wrongdoing.
It is unlikely they will be given the maximum sentence, the death penalty, if found guilty. But they are likely to face many years in prison, our correspondent says.
This trial is seen by many as a showcase of the government's intolerance against political dissent in the run-up to next year's Communist Party Congress.
Mr Dinh rose to prominence when he represented Vietnam's interests in the so-called "catfish battle" where US farmers accused the Vietnamese of dumping cheap seafood on the US market.
In recent years, Mr Dinh defended some of Vietnam's leading human rights and democracy activists, such as fellow lawyers Nguyen Van Dai and Le Thi Cong Nhan, who have also been jailed for anti-government activity.