Sergeant Omer Halisdemir killed Brigadier General Semih Terzi on the night of July 15, 2016, breaking the command chain of the plotters.
An Ankara court, which heard the case, found all 18 guilty of "deliberately killing" the soldier as well as "attempting to destroy the constitutional order" by seeking to oust the government, the Anadolu news agency reported.
Halisdemir shot Terzi dead outside special forces headquarters in Ankara. He was then himself killed by the plotters.
After the shooting, Halisdemir has become a national hero with parks, schools and other public places named after him.
His tomb in the central Anatolian region of Nigde has also become a major place of pilgrimage for visitors.
Anadolu reported Thursday that Omer in 2017 was now one of the three most popular names for boys in Turkey.
The government blamed Muslim preacher Fethullah Gulen for masterminding the failed coup. Gulen, who lives in self-imposed exile in Pennsylvania, strongly rejects the charges.
Turkish authorities have cracked down on alleged coup plotters in the wake of the attempted putsch, with over 55,000 people either jailed or in custody awaiting the outcome of their trials.
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