Born Prunella Jane Ransome in Croydon, Surrey, she later lived in Titchfield where her father Jimmy Ransome was a public school headmaster from 1952 to 1958. Ransome studied at Elmhurst School for Dance and began her performing career as a teenager. Ransome made her West End debut in a 1959 musical production of Jane Eyre with further West End appearances in Do Re Mi and Oliver!. She later spent five months singing at a cabaret in Athens and upon returning to the UK worked delivering cars for a London automobile dealership prior to being cast in 1965 in the musical stage play The Match Girls. Following that play’s 1966 West End transfer, Ransome’s performance drew the attention of a producer of the film Far from the Madding Crowd, with a screen test leading to her playing that film’s second female lead and her performance earning her a Golden Globe Award nomination. Ransome progressed in her film career playing the female lead in the 1969 film Alfred the Great. Her subsequent screen career, however, was focused almost exclusively on television, Ransome having debuted in that medium in the 1967 serialization of Kenilworth. In the 1970s she had major multi-episode roles in three well-regarded TV drama series: Warship and A Horseman Riding By for the BBC; as well as Dangerous Knowledge for Southern Television. She also appeared in other TV series of the period.

Ransome’s rare film roles included the female leads in the 1971 western Man in the Wilderness and in Narciso Ibáñez Serrador’s Who Can Kill a Child?, a 1976 horror film which has become a cult favorite. She also played the female lead in the 1980 TV mini-series Seagull Island which was re-edited into the film The Secret of Seagull Island (1981). Ransome retired as a career actress following her participation in the 1984 television series Sorrell and Son, though she made occasional television guest appearances in the 1990s. She had two daughters, Charlotte (born 1973) and Victoria (born 1975) and was aunt to Thomas Ransome. In 1980 Ransome relocated from London to Suffolk. She died of natural causes in Norwich on 4 March 2002.