Turkey's Constitutional Court on Tuesday rejected rights defender Osman Kavala's appeal for immediate release pending trial, narrowly ruling that his detention immediately after acquittal was lawful.
A respected figure in international circles, Mr Kavala, 63, has been in prison for over three years despite being acquitted in February in connection with the 2013 anti-government protests.
He was immediately re-arrested and jailed on fresh charges of espionage and involvement in a failed 2016 coup against President Recep Tayyip Erdogan.
It had been thought that Turkey may choose to release Mr Kavala as part of efforts to open a new page in relations with the European Union.
In a bid to repair Turkey's global international image in the middle of a deep economic downturn, Mr Erdogan last month pledged to push through judicial reforms that secured broader independence of the courts.
But he also took personal aim at Mr Kavala, saying he was responsible for the 2013 protests – even after being cleared of involvement in court.
"We can never be with financiers of Gezi events," Erdogan said, referring to demonstrations against plans to demolish a park in the heart of Istanbul that snowballed into nationwide protests.
"We can never be with Kavalas," Erdogan said.
Mr Kavala, a businessman and philanthropist, held on pre-trial detention since being detained at an Istanbul airport in October 2017, faces life in prison for seeking to overthrow the constitutional order and a further 20 years if convicted on additional espionage charges.
The next hearing is scheduled for February 5.
The official Anadolu news agency said the Constitutional Court ruled by an 8-7 margin that Mr Kavala's ongoing detention did not breach his rights to liberty and security.
The ruling is expected to be published later.
Human rights advocates see Mr Kavala's case as a bellwether on the state of political freedoms under Erdogan's rule and say the charges against him are politically motivated.
Born in Paris, Mr Kavala was a founding member of philanthropist George Soros' Open Society Foundation in Turkey. He headed Anadolu Kultur, a group that promoted cross-cultural ties through the arts, at the time of his arrest.
In a court appearance this month, Mr Kavala rejected the charges, telling the presiding judge: "I have opposed military coups my entire life and have criticised the army's interference in politics."
On December 18, Istanbul’s 36th High Criminal Court rejected an appeal by Mr Kavala and extended his pre-trial detention period.
The European Court of Human Rights first called for Mr Kavala's "immediate release" in December 2019.
Mr Erdogan branded Mr Kavala the "red Soros of Turkey" a few days after he was first detained.
US academic Henri Barkey is being tried in absentia alongside Mr Kavala in the new trial.
The accusations against Mr Barkey stem from a conference he organised about Iran on an island off Istanbul at the time of the 2016 coup attempt.
The charge sheet alleges Mr Barkey used the event as cover to coordinate the putsch with Kavala.
Mr Barkey told AFP this month that the charges against him were "a travesty of the first order".