Gwynne was especially convincing as quirky or somewhat melancholy authority figures, his dour looks, deep voice, deliberate delivery and sometimes prissy manner were well utilized in a number of films including "On the Waterfront" as longshoreman Slim (1954); Bernardo Bertolucci's "Luna" (1979) in a cameo as Jill Clayburgh's ill-fated husband; "The Cotton Club" (1984) as a sympathetic underworld figure; "The Boy Who Could Fly" (1986), as the alcoholic uncle of the title character; "Pet Sematary" (1989) as a country gentleman; a bit part in Woody Allen's "Shadows and Fog" (1992); and a delicious final supporting role as a no-nonsense Southern judge in "My Cousin Vinny" (1992).
Gwynne also had a significant career on the New York stage appearing various plays including "Irma La Douce", "Texas Trilogy", "Arsenic and Old Lace", "Twelfth Night" and "The Winter's Tale". Gwynne worked as an advertising copywriter in the late 50s while pursuing acting. In the 80s, he made a good deal of his income doing voice-overs for TV commercials. A children's book author and illustrator, Gwynne succumbed to pancreatic cancer at age 66.