Giovanni Strangio was accused of planning and carrying out the killings that shocked Germany and threw a spotlight on the international network of one of Italy's most secretive and powerful crime syndicates – the 'Ndrangheta. Seven others were also sentenced to life.
The killings were the result of a long-running vendetta between rival families in the town of San Luca in the southern Italian region of Calabria, a 'Ndrangheta bastion, which has left 16 people dead since the 1990s.
A cycle of reprisals between the Nirta-Strangio and Pelle-Vottari clans led to the murder of Maria Strangio, the clan leader's wife, on Christmas Day 2006.
Giovanni Strangio, now 31, brought a gun to her funeral and was lightly injured in an exchange of fire with members of the rival clan.
Prosecutors said he planned the Duisburg killings as revenge while running a pizzeria in the town of Kaarst in west Germany.
Following the massacre outside the Da Bruno restaurant, Strangio was arrested in 2009 in the Netherlands where had been hiding and extradited to Italy to face trial in Locri in his native Calabria region.
The Duisburg killings "were the result of deep-rooted and blind hatred that accumulated as years went by," the prosecutor had said in closing remarks. The victims in Germany were men between the ages of 17 and 39.
"Justice has been done," said Maria Carlino, the mother of two brothers killed in the massacre. "By killing my two sons, they took everything away from me. They destroyed our lives taking away what we held most dear."
There was chaos in the courtroom when the sentences were pronounced.
A female relative of the defendants screamed and banged her fists on a table, ANSA news agency reported. She was later seen fighting with police officers and reciting prayers as she was dragged out of the hearing.
Following the verdict, prosecutor Giuseppe Pignatone said: "It's very important to have shed light on one of the most brazen crimes of recent years which showed the gravity of the clans' presence outside Italy."
The 'Ndrangheta has a major international drug-trafficking network estimated to generate billions of euros in revenue every year. Its tight-knit family structure has proved difficult for police to infiltrate.