They were given "aggravated life sentences", which come with tougher terms than a normal life sentence, BBC reported on Tuesday.
The country's president had previously said he backed reintroducing the death penalty for coup plotters. The failed coup to overthrow President Recep Tayyip Erdogan left at least 260 dead and 2,200 injured on 15 July 2016.
The Turkish government has since led a crackdown on alleged coup supporters, with the dismissal of more than 150,000 state employees and the arrest of some 50,000 people.
Of the 280 ex-military people on trial, the court in Izmir also served lesser sentences to a further 52 defendants.
Sitting in Izmir in western Turkey, the court gave 21 people 20 years in prison for "assisting the assassination of the president", while 31 others were sentenced to between seven and 11 years for "membership of a terrorist organisation", state news agency Anadolu reported.
President Erdogan had backed reintroducing the death penalty for coup plotters. He also said they should wear Guantanamo Bay-style uniforms. Turkey abolished the death penalty in 2004.
The Turkish authorities accused a movement loyal to the Muslim cleric, Fethullah Gulen, of organising the 2016 plot.
Gulen, who has been in self-imposed exile in the US since 1999, denies any involvement, and Washington has so far resisted calls from the Turkish authorities to extradite him.
Rebel soldiers had attempted to overthrow the government overnight and plotters tried to detain Mr Erdogan as he holidayed in an Aegean resort.
However, he had left 15 minutes before and the coup was thwarted by civilians and soldiers loyal to the president.
A purge followed the coup, in which thousands of public employees from police officers to teachers were sacked or arrested under suspicion of stirring up dissent.
Erdogan's critics say he is using the purge to stifle political dissent.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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