The 26 suspects are all leaders of Taksim Solidarity, an umbrella group of civil society, union and political groups that was at the forefront of demonstrations marking the biggest challenge yet to the government.
The activists, who include doctors, architects and engineers, had been charged with including founding a crime syndicate, violating public order and organising illegal protests through social media and faced years in prison.
"All of us were acquitted," Mucella Yapici, one of the leaders, told AFP. "It was an absurd case which meant to declare Taksim Solidarity a criminal organisation."
The suspects went on trial at an Istanbul court in June 2014 a year after the protests which started as a small environment battle to save Gezi Park -- one of the few green spots in the country's mega city.
The protests snowballed into a nationwide wave of anger against Erdogan, who was then prime minister, and were ultimately put down by the police.
Rights campaigners had called for the charges to be dropped, with Amnesty International calling the process a "politically motivated show trial".