Died June 26, 2012. Born September 28, 1919.

American actress, perhaps best remembered as Lucy Ricardo's frenemy, the stuck-up Carolyn Appleby, in I Love Lucy.

The New York City-born Singleton began her career in show business as a vocalist in the late 1930s with Art Jarrett's orchestra and as a dancer for three seasons with the New York City Ballet. Singleton distinctive voice made her a favorite in the radio industry. During a guest appearance on the radio show My Favorite Husband in 1948 she met Lucille Ball and began their lifelong friendship. Singleton made her television debut in a 1953 episode of The Adventures of Superman. Later that year, she made an appearance on I Love Lucy playing Carolyn (initially referred to as "Lillian") Appleby. Singleton appeared on I Love Lucy a total of nine times. In 1966, Singleton was teamed again with Ball on The Lucy Show in the episode, "Lucy and Art Linkletter", in which she played Miss Cosgrove, an actress whom Linkletter hires to help Lucy with a stunt on his TV show. In an interview in "The Lucy Book" by Geoffrey Mark Fidelman (Renaissance Books, p. 233), Singleton revealed that she had originally been hired to be a regular on Ball's third series, Here's Lucy, in 1968. Ball would have played a dumb secretary and Singleton the more intelligent one, but the premise was dropped when Ball decided to cast her own children in the show. She did, however, appear in the series premiere episode, "Mod, Mod Lucy". In 1970, Singleton was featured on an episode of the ABC-TV 1970-1971 sitcom, Make Room For Granddaddy (an updated version of The Danny Thomas Show) which had Lucille Ball as the guest star. In this installment, titled "Lucy Carter, Houseguest", Singleton played Grace Munson, another character from I Love Lucy. Her final appearance on Here's Lucy was in 1974 as Lucille Ball's studio secretary in an episode titled "Lucy (Carter) Meets Lucille Ball". Singleton and Ball were reunited one last time, again as Lucille Ball's studio secretary, in the 1980 special Lucy Moves to NBC.

Singleton guest starred on several other television shows including Hogan's Heroes, The Dick Van Dyke Show and The Twilight Zone, all on CBS, and on Rod Cameron's syndicated modern western crime drama, State Trooper. She played Laura, the girlfriend of Butch Cassidy on a 1958 episode, "The Outlaw Legion," of the syndicated western Frontier Doctor. Singleton played the sympathetic neighbor, Susie, to Annie Fargé's scatterbrained character Angel Smith in the short-lived CBS sitcom Angel (1960–61). She also appeared in All in the Family as Edith's hotel roommate, Lydia Stonehurst, in the well-remembered 1971 episode "Edith has Jury Duty." Further, she played in two Perry Mason episodes, titled "The Crooked Candle" and "The Purple Woman".

Singleton also has the distinction of having guest starred on the Fred MacMurray sitcom My Three Sons playing two different characters who had recurring roles throughout the long run of the show. She originally played the mother of Meredith MacRae whose character Sally Morrison married original oldest son Mike Douglas (Tim Considine) in the 1964-65 season. Later she played Margaret, mother of Polly Williams (Ronne Troup) in the 1970-71 season.

At the time of her death in June 2012, Singleton was one of two recurring adult cast members from the I Love Lucy show still living (the last remaining one Shirley Mitchell, who played Marion Strong). In 2001, Singleton took part in festivities honoring the 50th anniversary of the show, and in 1999, she participated in a panel discussion concerning the life and legacy of Lucille Ball at a Loving Lucy convention in California. Her last acting role was in Deadly Messages (1985).

Singleton was widowed and childless, and she resided in the Greater Los Angeles area. She was not related to actress/voice artist Penny Singleton (née McNulty). Singleton died on June 26, 2012 in her Los Angeles, California home from unknown causes. She died one day earlier than Don Grady, her costar in My Three Sons.