[1] Singleton worked in New York during World War II both as a guest star and in regular roles on numerous hit radio shows, including The Whistler and The Alan Young Show,[2] on which she played Young's girlfriend, Betty Dittenfeffer.

[3]: 97 During a guest appearance on the radio show My Favorite Husband in 1948 she met Lucille Ball and began their long professional relationship.

In 1953, she made her television debut as Gloria Harper in the episode "Jungle Devil" on the series, The Adventures of Superman.

In 1970, Singleton was featured on an episode of ABC sitcom, Make Room For Granddaddy (an updated version of The Danny Thomas Show) which had Lucille Ball as the guest star.

Singleton also appeared on numerous other television shows including Richard Diamond, Private Detective, The Dick Van Dyke Show, Pete and Gladys, Hazel, The Real McCoys, The Twilight Zone, The Munsters, The Fugitive, Dynasty, Phyllis, Family Affair, Hogan's Heroes, Gomer Pyle: USMC, State Trooper, Gunsmoke, and Frontier Doctor.

At the time of her death in June 2012, Singleton was the last surviving major recurring adult cast member from the "Lucy" shows.

Her last major acting role was in Deadly Messages (1985), though she appeared in advertising and voice overs for many subsequent years, most notably in recurring ads for Hills Brothers' Coffee.