Snowden, 33, who exposed the US global surveillance scheme, was granted temporary asylum in Russia for one year in 2013 and later received a three-year residence permit. His whereabouts in Russia are a closely-guarded secret.
In the United States, he faces up to 30 years in prison on charges of espionage and theft of government property. Snowden repeatedly said he would return to the United States if Washington guaranteed him a fair trial.
The award was established by the citizens of Kassel in 1990 to honor individuals for their contribution to the ideas of Enlightenment.