Kay was born Adrianne Judith Pringle in Blackburn, England, the daughter of Ethel (Hesmondhalgh) and James S. Pringle. When she was young, her mother died, and after living briefly with the family of her cousin Margaret Tomlinson, she was adopted by the Cheetham family (then living in Preston, Lancashire). Karen's adoptive father Victor (Vic) Cheetham was a fighter pilot in World War II; he served in Burma with RAF 113 Squadron flying Hurri-bombers, supporting the infantry in a very successful action around Dimapur and Palel in 1944.
Judith, as she was then known, made her professional debut in the Black and White Minstrel Show, Blackpool, when she was 16. It was about this time that she adopted the stage name Karen Kay.
On 30 December 1969 while living in Stretford, Greater Manchester, she gave birth to twin boys, Jason and David, fathered by Luís Saraiva. A few weeks after birth, David died. Jason would later become the vocalist and frontman of British acid jazz group Jamiroquai in 1992, under the stage name Jay Kay.
Karen Kay became a regular guest at the Starlight Club in Little Harwood, and was tipped as The Face of 1979. She worked together with Lenny Henry and David Copperfield on a TV series entitled Six of a Kind, which later was produced without her under the title Three of a Kind.
Karen Kay has appeared and acted in Lennie and Jerry (1979), Des O'Connor Tonight (1981), Max Bygraves Side by Side (1982), The Bob Monkhouse Show (1983) and Aspel and Company (1985). She had her own television series, Karen Kay, in 1983.