During World War II, he served in the Army Special Services Branch entertaining the troops before moving west in 1946 to pursue acting and complete his education.

Flynn gained local celebrity as a director by guiding the Canfield Players in such productions as Harvey, Antigone and Pursuit of Happiness.

[citation needed] After appearing in a number of stage plays, Flynn returned to Youngstown, where in 1950 he conducted an unsuccessful campaign for a seat in the Ohio Senate as a Republican.

He played Mr. Kelley in 15 episodes of The Adventures of Ozzie and Harriet and appeared in other classic series such as The George Burns and Gracie Allen Show, The Twilight Zone, Gunsmoke (S4E27 as Onie Becker & S8E10 as “Liquor Drummer”) and Make Room for Daddy.

His appearance on March 30, 1961, was a patriotic program set at sea on the aircraft carrier USS Yorktown, to celebrate the 50th anniversary of naval aviation.

From 1962 to 1966, Flynn played the irascible Captain Wallace "Wally" Burton Binghamton (also known as "Old Leadbottom") on ABC's McHale's Navy in all but one episode, in which he became known for his exasperated catch phrases "What is it, What, WHAT, WHAT!?

[3] In the early 1970s, Flynn spearheaded a movement on behalf of the Screen Actors Guild for more equitable distribution of TV residual payments.

On July 19, 1974, shortly after Flynn completed voice-over work as Mr. Snoops for Walt Disney's animated feature film The Rescuers (released in 1977), his body was discovered by family members in the swimming pool of his Beverly Hills home.

[7] His June 13, 1974, taping of The Merv Griffin Show had been announced for broadcast on July 19, prior to Flynn's death the same day, proving to be his final appearance.