The men were arrested in 2014 after killing a soldier, a policeman and a truck driver in an armed attack in Nigde, central Turkey.
The incident is viewed as the first act of violence carried out by members of the Islamic State group inside Turkey and raised awareness of the threat the organization poses to the country.
Since then, authorities have blamed IS for major bombings in the border town of Suruc and the capital Ankara, as well as attacks on tourists in Istanbul.
Ali Cil, the lawyer of the civilian victim, said they were also found guilty of wanting to overthrow the government by force.
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Ramadani received five aggravated life sentences, Xu four, and Zakiri one. An aggravated life sentence is the worst possible penalty in the Turkish criminal code. Prisoners serving such sentences are kept in solitary cells and have only one hour exercise per day. They are not eligible for pardons or conditional release.
The three men were also sentenced to more than 124 additional years each behind bars and fined $77,000 each. "I hope they rot in jail," said the killed soldier's mother, Hatice Kozanoglu.
Turkey shares long borders with Syria and Iraq, two war-torn nations where IS controls large pockets of territory. The porous nature of those borders has made Turkey a natural stepping stone for jihadi fighters.
Turkey, a member of the US-led coalition against IS, has stepped up controls at airports and land borders and deported thousands of foreign fighters. But it is struggling to tackle the threat of IS militants who have cells inside Turkey and sometimes fire into the country from across the Syrian border.