His paternal grandfather, Walker Gwynne, was an Anglican priest, born c. 1846 in Camus, County Tyrone, Ireland, who married American Helen Lea Bowers.

[1][2] Although Gwynne partially grew up in Tuxedo Park, New York,[3] he spent most of his childhood in South Carolina, Florida, and Colorado because his father traveled extensively.

[5] Having attended high school during World War II, Gwynne joined the United States Navy after graduation, serving as a radioman on submarine chaser USS Manville (PC-581).

To support himself, Gwynne worked as a copywriter for the J. Walter Thompson advertising agency, resigning in 1952 upon being cast in his first Broadway role, a gangster in a comedy called Mrs. McThing starring Helen Hayes.

[citation needed] A talented vocalist, Gwynne sang in a Hallmark Hall of Fame television production The Littlest Angel (1969), and went on to perform in a variety of roles on stage and screen.

In 1974, drawing upon his own Southern roots, he appeared in the role of Big Daddy Pollitt in the Broadway revival of Cat on a Hot Tin Roof with Elizabeth Ashley, Keir Dullea and Kate Reid.

In 1984, Gwynne auditioned for the part of Henry on the sitcom Punky Brewster, then withdrew in frustration when a director identified him as Herman Munster rather than by his real name.

[18] Gwynne's performance as Jud Crandall in Pet Sematary was based on author Stephen King, who is only an inch shorter than the actor, and uses a similarly thick Maine dialect.

The character's likeness and accent, as played by Gwynne, have been used in a number of episodes of the animated show South Park, beginning in 2001 and as recently as 2019.

[19] Gwynne also had roles in the movies Simon, On the Waterfront, So Fine, Disorganized Crime, The Cotton Club, Captains Courageous, The Secret of My Success, Water, Ironweed, Fatal Attraction, and The Boy Who Could Fly.

[20] In addition to his acting career, Gwynne sang professionally, painted, and wrote and illustrated children's books, including Best in Show (later titled It's Easy to See Why), Daddy Has a Mole on His Nose, A Chocolate Moose for Dinner, The King Who Rained, Pondlarker, The Battle of the Frogs and Mice, and A Little Pigeon Toad.

[9] Initially the books did not achieve wider popularity because their format was geared to a very young audience, but the concept was more appealing to older children and adults.

[citation needed] In 1952, Gwynne married socialite Jean "Foxy" Reynard,[21] a granddaughter of New York City mayor William Jay Gaynor.