Castellano gained worldwide fame for his role in Lovers and Other Strangers (1970), for which he was nominated for an Academy Award. He achieved further stardom in 1972 for playing the part of Peter Clemenza, in The Godfather. The Godfather became the highest-grossing film up to that time. Castellano, along with several other cast members, became widely known from the popular film. He spoke one of the film's most famous lines, "Leave the gun; take the cannoli," which he partially ad-libbed.