Kavala and eight others accused of organizing the Gezi Park protests, which began in Istanbul, were acquitted of all charges in February 2020 but an appeals court overturned that ruling in January.
Kavala, who has been kept in detention for three-and-a-half years, is also accused of involvement in a 2016 coup attempt. Those charges were combined with the Gezi case in February.
The European Court of Human Rights called in December 2019 for his release on grounds the detention aimed to silence him. But Turkey has not abided the ruling despite repeated calls by the Committee of Ministers of the Council of Europe.
The United States also called for his release in February.
"Each phase of this case is riddled with injustices, inconsistencies and illogical and unlawful procedures," said a campaign group called Free Osman Kavala.
Re-opening the Gezi case has become "a source of embarrassment not only for the government and the judiciary but also for the country as a whole," it said.
Critics say Turkey's judiciary has been exploited to punish President Tayyip Erdogan's perceived opponents, especially under a crackdown after the 2016 coup attempt. The president and his AK Party say the courts make independent decisions.
The case of seven others who were abroad during the initial trial was joined again this month for the re-trial.
Some of the defendants had also been acquitted in 2015 of charges related to the Gezi protests, meaning they are being tried over the same events for a third time.
ERDOGAN
The Gezi demonstrations in the summer of 2013 started as a protest against the redevelopment of a park in Istanbul, a city with limited green space, and quickly spread across the country.
Erdogan, then Turkey's prime minister, dismissed the idea they were environmentally motivated and said they aimed to topple his government. The defendants deny the charges against them.
The indictment calls for life sentences without parole for the defendants, who are accused of attempting to overthrow the government and financing the protests among other charges.
In response to questions from Reuters in March, Kavala said: "The claim that I planned, directed and financed the Gezi protests was an extremely fantastical one."
The allegations that he was involved in the 2016 coup attempt "much more absurd," Kavala added. "These are properly surrealist fiction. They are impossible to falsify because they are not based on any evidence, concrete fact or reality."