Christie was born on 14 April 1940[2][3] at Singlijan Tea Estate, Chabua, Assam, British India, the elder child of Rosemary (née Ramsden), a painter, and Francis "Frank" St. John Christie.[4] Her father ran the tea plantation where she was raised.[4] She has a younger brother, Clive, and an older (now deceased) half-sister, June, from her father's relationship with an Indian woman, who worked as a tea picker on his plantation.[5] Frank and Rosemary separated when Julie was a child.
She was baptised in the Church of England and studied as a boarder at the independent Convent of Our Lady school in St. Leonards-on-Sea, East Sussex, after being expelled from another convent school for telling a risqué joke which reached a wider audience than originally anticipated. After being asked to leave the Convent of Our Lady as well, she later attended Wycombe Court School, High Wycombe, Buckinghamshire, during which time she lived with a foster mother from the age of six.[6]
After her parents' divorce, Christie spent time with her mother in rural Wales.[6] As a teenager at the all-girls' Wycombe Court School, she played "the Dauphin" in a production of Shaw's Saint Joan. She later studied at the Central School of Speech and Drama.[7]