A Turkish court rejected on Tuesday an appeals court order to retry a lawmaker from the main opposition party, upholding his 25-year jail term, CNN Turk reported.
Enis Berberoglu became a symbol for more than 50,000 people detained in the wake of a failed coup in July 2016.
The chairman of his secular Republican People's Party (CHP) held a 425 km (265 mile) protest march from the capital Ankara to Istanbul when Berberoglu was convicted and sentenced in June for military espionage.
The court had said Berberoglu gave an opposition newspaper a video purporting to show Turkey's intelligence agency trucking weapons into Syria.
The penal court had been ordered to retry Berberoglu last month, but it refused the order saying the upper court's decision to overturn was against procedure and law.
Berberoglu was the first CHP lawmaker to be jailed in a crackdown by President Recep Tayyip Erdogan's government that has raised concerns among Turkey's Western allies and rights groups.
More than 150,000 people, including teachers, academics and lawyers, have also been suspended from their jobs.