Prosky appeared in Thief, Christine, Hanky Panky, The Natural, Hoffa, Broadcast News, Things Change, The Great Outdoors, Loose Cannons, Rudy, Mrs. Doubtfire, Green Card, and Dead Man Walking. In addition to appearing in films, Prosky appeared as a regular on Hill Street Blues, Danny, and Veronica's Closet. He was considered for the role of Martin Crane in Frasier and later made a guest appearance in the series as a reclusive Writer. He portrayed Rebecca Howe's father on Cheers; on the same show, he was offered the role of Coach Ernie Pantusso, but turned it down. Prosky also portrayed Jake "the Snake" Connolly on a 2-part 1991 episode of Coach.