Police fired tear gas at protesters outside the court in a town near Istanbul as the verdicts were being delivered in the highly-divisive case.
Ex-military chief Ilker Basbug, along with several other army officers, were sentenced to life in prison, while 21 people were acquitted, according to the verdicts issued so far.
The trial has been seen as as a key test in Prime Minister Recep Tayyip Erdogan's showdown with secularist and military opponents during his decade-long rule.
Tensions were high outside the high-security tribunal in the town of Silivri, near Istanbul, and hundreds of riot police fired tear gas to disperse some 1,000 protesters who had evaded a police barricade and attempted to march on the courthouse, an AFP reporter said.
Istanbul governor Huseyin Avni Mutlu had on Friday said that demonstrations outside the court would not be allowed.
"This trial is purely political," Mustafa Balbay, one of the defendants, told an audience of MPs and journalists inside the courtroom.
"Today it's the government which is convicted, not us."
Basbug, 70, led Turkey's military campaign against the rebel Kurdistan Workers' Party (PKK) for many years, only to find himself accused in his retirement of having led a terrorist group himself.
The verdicts come after Turkey was rocked in June by mass protests that presented Erdogan's government with its biggest public challenge since it came to power in 2002.
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