McGrath was nominated two years in a row (1989 and 1990) for a Gemini Award for My Secret Identity. The first time was for Best Performance by a Lead Actor in a Continuing Dramatic Role, and the second time was for Best Writing in a Dramatic Series (shared with Michael O'Connell, father of My Secret Identity lead Jerry).

McGrath was born in Timmins, Ontario. He is known for his roles in Cheers as "Andy-Andy" Schroeder (the would-be strangler of Diane Chambers), Dr. Benjamin Jeffcoate in My Secret Identity, Crewman Chell in Star Trek: Voyager, and as Dr. Derek Hebert in Doc. McGrath also played Buck the dog in a fantasy sequence in a second-season episode of Married... with Children and a mutant in the 1993 comedy film Freaked. He most recently appeared in a recurring role as the character of Anglican priest Duncan Magee in the CBC Television sitcom Little Mosque on the Prairie seasons 1-3; in season 4 (beginning late September 2009), he appears to have been written out and replaced with a younger priest played by actor Brandon Firla. He voices Spiff in the animated children's series Iggy Arbuckle. He also voices Melvin, the mayor of Maple Lake in the animated series Bob & Doug. He also provided the voice of Heathcliff's nemesis Spike in DIC's Heathcliff and the Catillac Cats. He has also voiced various characters in Grossology, Pole Position, The Romance of Betty Boop, Intergalactic Thanksgiving, Bakugan Battle Brawlers, Super Why!, Wayside, Ruby Gloom, Toot and Puddle, Spliced, Jane and the Dragon and Take Me Up to the Ball Game. In 2002, he narrated the National Film Board of Canada short The Hungry Squid, which won the Genie Award for Best Animated Short. In the 1970s, he was a prominent actor on TVOntario educational programming, most notably Mathmakers. He currently voices Mr. McFeely in Daniel Tiger's Neighborhood and Chief Quimby in Inspector Gadget. McGrath has appeared on new CBC series Kim's Convenience as Frank the handyman.