The Istanbul court ruling ends the long-running legal saga which began in October 2012 when Say went on trial on charges "insulting religious beliefs" in a series of Twitter posts.
In a hugely convoluted process, the Turkish classical star was initially handed a 10-month jail sentence in 2013 before a retrial was ordered the same year in which he received an identical sentence.
But the Supreme Court of Appeal in October 2015 overturned the sentence, sending it back to a lower court for a final ruling.
The charismatic pianist -- who is also a renowned composer -- was prosecuted for Twitter posts in 2012 that allegedly attacked Muslims.
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Say, 45, has played with orchestras across the world including in Berlin, New York, Tokyo and Israel and regularly gives sold-out solo recitals that often mix Mozart with Turkish traditional sounds.
He has also served as a cultural ambassador for the European Union.
Last October, the appeal court ruled by a four-to-one majority that Say's comments should be viewed as "freedom of thought and expression and thus should not be punished".
"My client did not write an article neither did he show a film. He shared his opinions and retweeted opposing opinions. The real outrage was the opening of this case," Meltem Akyol said, quoted by Dogan news agency.
The case against Say, an atheist, caused consternation among secular Turks worried about what they see as a creeping Islamism under the ruling Justice and Development Party (AKP) co-founded by President Recep Tayyip Erdogan.
The government critic also previously accused Erdogan of being behind the case against him and in 2013 he called the charges "politically motivated".