Maurizio Tramonte, 65, a former secret service informant, was sentenced to life behind bars in 2015, 41 years after the attack that killed eight people and wounded 102 in Brescia in northern Italy.
He was run to ground in the Portuguese city of Fatima in June. Press reports at the time said he was nabbed by police as he prayed.
The former leader of the neo-fascist Ordine Nuovo (New Order) organisation, 82-year old Carlo Maria Maggi, was also given a life sentence for the attack on a trade union rally.
The bombing was one of a clutch of terror attacks by hardline rightwing and leftwing groups in Italy across more than a decade from the late 1960s.
That period of violent turmoil, which saw hundreds of killings, has been dubbed the "Years of Lead".
The Brescia attack was one of the worst in that troubled period along with the Piazza Fontana bombing in Milan in 1969, which killed 16, and the Bologna railway station blast which left 85 dead in 1980.
Bologna station in the aftermath of the 1980 bombing. Photo: AFP