Campbell was born in Streatham, London, England. Her mother, Valerie Campbell (née Morris), is a former ballet dancer of Afro-Jamaican descent. In accordance with her mother's wishes, Campbell has never met her unnamed father, who left then-18-year-old Valerie two months after the birth of their daughter.
Campbell is Black Jamaican and also of Chinese Hakka descent through her paternal grandmother of Chinese Jamaican ancestry (family name Ming).
Of her appearance, Campbell has said: "My features are completely ethnic, and I'm proud of them."