In 950, his father, King Berengar II of Italy, appointed him to rule in the familial margraviate.
In 959, Guy sheltered the exiled doge of Venice, Pietro III Candiano.
Guy brought Pietro to his father the king and then the two of them led an expedition against Theobald II, Duke of Spoleto.
Guy and Conrad joined with him in besieging Pavia, the Italian capital.
In 965, Guy was killed fighting an army of Swabians under Duke Burchard III.