Al-Rasafah Central Criminal Court in the capital Baghdad issued the verdict against Tarek Khayat this week over his role as a Daesh commander in Iraq, presstv. ir reported.
He was captured in the former Daesh stronghold of Raqqah in northwestern Syria earlier this year.
Under Iraqi law, Khayat has 10 days to appeal against the sentence, which did not include charges related to a plot to blow up an Etihad flight departing Sydney using a bomb concealed in a meat grinder and a Barbie doll.
The Australian Federal Police maintain that the 48-year-old directed his Sydney-based brothers to plant a bomb on the flight to Abu Dhabi in the United Arab Emirates in July 2017.
His brothers Khaled and Mahmoud, who are Australian citizens, are in custody over the plane bomb plot. They will face trial in the NSW Supreme Court next year.
The brothers are accused of planting the bomb in the luggage of a fourth brother, Amer Khayat, a Lebanese-Australian dual national.
The attack was foiled when Etihad check-in staff told Amer his bags were overweight.
Lebanese authorities arrested Amer 11 days after he arrived in Beirut, and he has been in custody since then. He has faced several hearings before a military tribunal, which is trying to work out his involvement in the alleged plot.
Tarek moved to Syria with his wife and five children in 2014. He was previously a high-ranking militant commander in the northern Lebanese city of Tripoli.
He is wanted by Lebanese authorities for his attempts to set up a Daesh redoubt in the country's north, and for leading his followers in battles against the Lebanese Army in Tripoli in 2014, shortly before he fled to Syria.