The actor is perhaps best well-known for his role as Frasier Crane's father Martin on "Frasier." He also appeared in more than 30 productions at Chicago's Steppenwolf Theatre.
Mahoney, who was born in England, later moved to Illinois in his youth. He attended Western Illinois University and received his master's degree in 1976. He later received an honorary degree from WIU in 2003.
Mahoney also created the John Mahoney Research Fellowship for English graduate students at WIU.