The 43-year-old, identified as Ibrahim A., led a 150-strong militia that controlled northeastern Aleppo, the Duesseldorf court said in a statement on the official legal website.
"As a commander he used lawlessness resulting from chaos of the civil war and his de facto control of parts of Aleppo for criminal gains, plundering and kidnapping people whom he tortured or allowed to be tortured by his militiamen," the statement read.
The convict amassed a fortune by claiming ransom, investigators found. He was arrested in Germany after a survivor recognized him. Ibrahim denies the charges. The court said the sentence can be appealed.