A leading Turkish rights defender expects to learn Monday if he can walk free after more than four years in jail without a conviction or will spend the rest of his days behind bars.

The case of Paris-born philanthropist Osman Kavala has gnawed on Turkey's ties with Western allies since his arrest in October 2017.

The 64-year-old was then best known as a soft-spoken businessman who was using a part of his wealth to promote culture and projects aimed at reconciling Turkey and its arch-nemesis Armenia.

But President Recep Tayyip Erdogan portrayed him as a leftist agent of the Hungarian-born US billionaire George Soros who was accused of using foreign money to try and topple the state.

He was first charged with funding a wave of 2013 protests that some analysts view as the genesis of Erdogan's more authoritarian streak.

That count did not stick.

A court acquitted and released him in February 2020 -- only for the police to arrest him before he had a chance to return home to his wife.

Another court then accused him of being involved in a failed but bloody 2016 coup attempt that unleashed a years-long crackdown in which tens of thousands were either jailed or stripped of their government jobs.

Kavala now stands accused of both charges.

His treatment has prompted the Council of Europe to launch rare disciplinary proceedings that could ultimately see Turkey's membership suspended in the continent's main human rights group.

"The fact that I have spent four-and-a-half years of my life in prison is a loss that cannot be compensated," Kavala told the court in a closing statement issued Friday by video link from his high-security prison outside Istanbul.

"The only thing that would console me is the possibility that what I have gone through helps put an end to grave judicial mistakes."

'Judicial prosecutions'

Kavala's fate will be determined by a panel of three judges who had regularly voted to keep him locked up pending trial.

Each hearing has been attended by a bevy of foreign diplomats who are trying to press home the continued importance of rights issues to Ankara's ties with the West.

"His unconditional release may mark a turning point in the de-politicisation of judicial prosecutions in Turkey," Amnesty International's Turkey researcher Guney Yildiz told AFP.

"That's why the result of this emblematic case is quite serious."

Kavala could be jailed for life without the possibility of parole if he is found guilty of spying and trying to topple the state.

Seven other defendants still in Turkey are also being tried in connection with 2013 protests that sprung up in defence of a small Istanbul park before morphing into a national movement.

Defendant Mucella Yapici -- also facing the threat of life in jail without parole -- told the court that the 2013 rallies were the "most democratic, most creative and peaceful collective movement in this country's history".

Monday's hearing will start with closing statements from defence attorneys. The three judges are expected to issue their verdict later in the day.

But the case's importance to Turkey's broader diplomatic standing has been slightly muted by Russia's two-month assault on Ukraine.

Erdogan has tried to leverage his good ties with both Moscow and Kyiv to try and mediate an end to the war.

His efforts have already seen a marked improvement in Ankara's relations with Washington that could soon see Turkey supplied with US military jets.

The hearing on Monday will be held in Istanbul at the same time as UN Secretary General Antonio Guterres meets Erdogan in Ankara before travelling to Moscow and Kyiv later in the week.