(1948) Vincent is the illegitimate son of Sonny Corleone and Lucy Mancini. (This plotline is exclusive to the movie, as it directly contradicts Puzo's original storyline, in which Lucy tells Tom Hagen she is not pregnant when he questions the motive for her suicide attempt). Vincent has never been treated as a real member of the Corleone family and so is never given access to the family's criminal empire. He endears himself to his uncle, Michael Corleone, by trying to protect him from rival Mafia families, and the aging Don takes the hot-headed young man under his wing.

Vincent saves Michael from an assassination attempt orchestrated by rival Joey Zasa, whom Vincent then personally murders. Vincent's irrepressible violent streak often angers Michael, but not nearly as much as his burgeoning romance with Michael's daughter (and Vincent's cousin) Mary, whom Michael fears would be endangered by being involved in Corleone family business.

Despite their personal differences, Michael appoints Vincent the new Don and head of the Corleone family. His time spent with Michael has made him into a new man: much wiser, patient, and aware of his status as the new Don. In return for being elevated, Vincent ends his relationship with Mary. The same night the romance ends, however, Mary is killed in an assassination attempt on Michael. Vincent quickly kills the assassin responsible.