She grew up in Hackney where her childhood was spent in poverty, with her parents splitting when she was fifteen and she was a mother by the age of seventeen. She attributed her maturity to becoming a mother, stating that she "grew up overnight" and that she "changed and became a better person because of it".
She found success at the age of 24 and enjoyed chart hits with her sister Melanie as Mel & Kim. Between 1986 and 1988 they had four huge hits, all written and produced by Stock Aitken Waterman, including a number one UK single with "Respectable", although they had stopped performing and recording in 1987 due to Mel's illness. When her sister Mel was diagnosed with cancer, Kim took time out of her career to nurse her for two and a half years until her death in January 1990.
With the aid of her boyfriend, ex-Bros bassist Craig Logan, Kim launched a solo career with much of her debut solo album composed of songs co-written with Mel, for what was intended to be the next "Mel and Kim" album. The album, Kim Appleby, contained her debut solo single "Don't Worry" which reached number two on the British charts in November 1990. A follow up single "G.L.A.D" was a UK #10 hit. Subsequent singles from her debut album were "Mama" [#19] and "If You Cared" [#44].
Kim's second album, Breakaway, was not a commercial success and had a limited release. She released three further singles, "Light Of The World [#41, 1993], "Breakaway" [#56, 1993], and reunited with Stock and Aitken on "Free Spirit" [#51, 1994]. A download only single called "High" was released in 2007.