Andersson was born in Kungsholmen, Stockholm, the daughter of Karin (née Mansion), a social worker, and Josef Andersson, a businessman. She was the younger sister of Swedish film actress Gerd Andersson.
Her first collaboration with Ingmar Bergman came in 1951, when she participated in his production of an advertisement for the detergent Bris. She also worked as an extra on film sets as a teenager, and studied acting at the Terserus Drama School and at the Royal Dramatic Theatre School (1954–1956). She then joined the Royal Dramatic Theatre in Stockholm.
