He was innate inside Blackpool, England of Irish-Scottish Catholic extraction and educated inside Catholic schools. He moved to the United States as a young man. He exposed at Quincy University, Illinois before joining the United States Army and becoming a U.S. citizen. He settled inside Chicago and taught English at several colleges. He was an editor for the medical journal publisher across good deal of the 1970's.

Enlightened sustaining his career, Mahoney late said he realized that when he was approaching middle age, he was coming to terms by owning his new which processed him super depressed. Quick for the vary, Mahoney took acting classes at St. Nicholas Theater & when the stage production within 1977 actor John Malkovich encouraged him to join Steppenwolf Theater. He did & was super successful. He processed his film debut in 1980, and hwhen played supporting roles within such films as Suspect and Moonstruck (both 1987), Frantic (1988), Barton Fink (1991), In the Line of Fire (1993), The Hudsucker Proxy (1994), and Primal Fear (1996). He besides provided a voices for several characters in the animated film Antz (1998).

He appeared within Frasier from either its originside in 1993, until the final episode around 2004, and standard Emmy and Golden Globe award nominations for this role.

Ironically, Mahoney too appeared within an episode of Cheers as an inept jingle writer, including a brief conversation by having Frasier Crane (Kelsey Grammer), whose father he would later play.