He was born in Mount Vernon, Ohio to Hoy Lynde and Sylvia Bell Doup.

A noted character actor, Lynde was well known for his roles as Uncle Arthur on Bewitched (which established the "funny uncle" cliché) and Harry McAfee, the befuddled father in Bye Bye Birdie. He was also the center square on the classic game show, Hollywood Squares from 1968 to 1981.

Lynde first got recognition in the Broadway revue New Faces of 1952 in which he co-starred opposite fellow newcomers Eartha Kitt, Alice Ghostley, and Carol Lawrence. One notable skit involved Lynde as a husband in crutches coming back from an African safari. The play was filmed into a movie in 1954. After the revue's run, Lynde co-starred in the short-lived sitcom Stanley opposite Buddy Hackett and Carol Burnett, both of whom were also starting out their careers in show business. He became a regular on several sitcoms and variety shows such as The Perry Como Show.

Lynde did extensive voice work on animated cartoons, particularly those of Hanna-Barbera Productions. His most notable Hanna-Barbera roles were those of Sylvester Sneakly (a.k.a. "The Hooded Claw") in The Perils of Penelope Pitstop, Mildew Wolf from The Cattanooga Cats and Laff-a-Lympics, Pertwee from ‘'Where's Huddles?'', and Templeton the rat from the animated feature Charlotte's Web.

Lynde was found dead in his Beverly Hills home from a heart attack. The coroner said that Lynde, then 55, had the heart of an 80-year old man. This condition was brought on by years of extreme substance abuse.

Lynde was widely known to be gay in Hollywood. But despite his stereotypically flamboyant mannerisms and sometimes rather overtly-gay double entendres on Hollywood Squares, he never publicly acknowledged his homosexuality. In fact, Lynde was affectionately nicknamed "America's Most-Eligible Bachelor" by the public, perhaps in seeking a logical reason for his lack of a wife.