Lofti Neb Nasr Amri, 42, was arrested at the Elmas detention centre in the Sardianian regional capital, Cagliari. He has also been fined 30,000 euros for drugs dealing.
He was sentenced in June 2005 by a court in Pistoia in the central Tuscany region. It was not clear from reports how he ended up at the Elmas centre.
The Elmas detention centre was the scene of a major riot staged last October by around 100 migrant inmates, which forced officials to close Cagliari airport, located just 150 metres from the centre.