Rabei Osman Sayed Ahmed, also known as "Mohamed the Egyptian", was arrested in Milan three months after the blasts that killed 191 people on March 11, 2004.
A court in Milan pronounced the verdict on Monday, Italy's Sky TG24 reported.
Sitting in a cage in the courtroom, Ahmed remained impassive as the verdict was read out.
A second Egyptian, Yahya Mawad Mohamed Rajeh, was sentenced to five years in jail in the case.
The pair were accused of belonging to an Egyptian group linked to al-Qaeda and of planning terrorist attacks within and outside Europe.
Spanish authorities indicated in September that they would request Ahmed's temporary extradition from Italy for a trial that is set to begin in February 2007.
During questioning by Spanish judge Juan Del Olmo in December 2005, Ahmed admitted to knowing some of the 25 suspects, most of them Moroccans, held over the Madrid attacks.
He is reported to have spoken about organising the attacks during telephone conversations with associates that were recorded by Italy's secret service.
Ahmed is understood to have been in Italy at the time of the blasts but spent time in 2003 in the Madrid district of Lavapies, home to several of the presumed bombers.
The cordinated bombing of four commuter trains, blamed on mainly Moroccan Muslim extremists, was the worst such attack in Europe since the downing of a PanAm jet over the Scottish town of Lockerbie which killed 270 people in December 1988.