Born in Boston, Massachussets, Cazale was coincidentally good friends with Al Pacino as a teenager. He moved to New York and became a messenger for an oil company, whilst appearing in small roles in Broadway productions on the side.
He won fame in The Indian Wants the Bronx in 1967, which won him an Obie Award, as well as bringing him to the attention of the makers of The Godfather, who thought he was ideal for the role of Fredo Corleone.
He later appeared in The Conversation, with Gene Hackman, and made a final appearance in The Deer Hunter, with Robert De Niro, dying from bone cancer before the film's release. Interestingly, every film he appeared in (living or dead) was nominated for the Academy Award for Best Picture. Additionally, all five films he appeared in involved either Al Pacino, Robert De Niro, or Francis Ford Coppola (or in the case of The Godfather Part II, all three).