Christie was born in 1941 in Singlijan Tea Estate, Chabua, Assam, India, then part of the British Empire, the first of two children of Rosemary (née Ramsden) and Frank St. John Christie. Christie's father ran the tea plantation where Christie grew up, and her mother was a painter from Hove. Christie has a brother and a half-sibling from her father's affair with an Indian mistress. Christie's parents separated during her childhood. She was baptized in the Anglican church and studied as a boarder at the independent Convent of Our Lady School in St. Leonards-on-Sea, East Sussex, from which she was later expelled. She then attended the independent Wycombe Court School in High Wycombe, Buckinghamshire, also living with a foster mother from the age of six. After her parents' divorce, Christie spent time with her mother in rural Wales. As a teenager at Wycombe Court School, she played the role of the Dauphin in a school production of George Bernard Shaw's Saint Joan. She later studied at the Central School of Speech and Drama before getting her big break in 1961 in a science fiction series on BBC television, A for Andromeda.

Christie's first major film role was in The Fast Lady, a 1962 romantic comedy. She first gained notice as Liz, the friend and would-be lover of the eponymous Billy Liar (1963) played by Tom Courtenay. The director, John Schlesinger, cast Christie only after another actress dropped out of the film.

It was 1965 when Christie became known internationally. Schlesinger directed her in her breakthrough role, as the amoral model Diana Scott in Darling, a role which the producers originally offered to Shirley MacLaine. Christie appeared as Lara Antipova in David Lean's adaptation of Boris Pasternak's novel Doctor Zhivago (1965), one of the all-time box office hits, and as Daisy Battles in Young Cassidy, a biopic of Irish playwright Seán O'Casey, co-directed by Jack Cardiff and (uncredited) John Ford. In 1966, the 25-year-old Christie was nominated for a BAFTA Award for Best Actress in a Leading Role when she played a double role in François Truffaut's Fahrenheit 451 and won the Academy Award for Best Actress and BAFTA Award for Best Actress in a Leading Role for Darling. Later, she played Thomas Hardy's heroine Bathsheba Everdene in Schlesinger's Far from the Madding Crowd (1967) and the lead character, Petulia Danner, (opposite George C. Scott) in Richard Lester's Petulia (1968).

In the 1970s, Christie starred in smaller, but culturally significant films such as Robert Altman's postmodern western McCabe & Mrs. Miller (1971), with Warren Beatty, where her role as a brothel 'madam' gained her a second Best Actress Oscar nomination, The Go-Between (again co-starring Alan Bates, 1971), Don't Look Now (1973), Shampoo (1975), Altman's classic Nashville (also 1975, in an amusing cameo as herself opposite Karen Black and Henry Gibson), Demon Seed (1977), and Heaven Can Wait (1978), again with Beatty. She moved to Hollywood during the decade, where between 1967 and 1974 she had a high-profile but intermittent relationship with Warren Beatty, who described her as "the most beautiful and at the same time the most nervous person I had ever known."

In 1979, she was a member of the jury at the 29th Berlin International Film Festival.

Following the end of the relationship with Beatty, she returned to the United Kingdom, where she lived on a farm in Wales. Never a prolific actress, even at the height of her fame and bankability in the 1960s, Christie made fewer and fewer films in the 1980s. She had a major supporting role in Sidney Lumet's Power (1986), but generally avoided appearances in large budget films and appeared in non-mainstream films. She narrated the 1981 feature documentary The Animals Film (directed by Victor Schonfeld and Myriam Alaux), a campaigning film against the exploitation of animals.

Christie has turned down many leading roles in films such as They Shoot Horses, Don't They?, Anne of the Thousand Days and The Greek Tycoon. Christie also signed on to play the female lead in American Gigolo opposite Richard Gere, however when Gere dropped out and John Travolta was cast in the role, Christie too dropped out from the project. Gere changed his mind and took back the role, however it was too late for Christie as her part was already taken by Lauren Hutton. Julie Christie also had to drop out of the leading role in Agatha due to breaking her wrist whilst roller-skating; the part was filled by Vanessa Redgrave.[citation needed]

Christie appeared as Gertrude in Kenneth Branagh's Hamlet. Despite her classical training as an actor, it was her first venture into Shakespeare. Her next critically acclaimed role was the unhappy wife in Alan Rudolph's domestic comedy-drama Afterglow, which gained her a third Oscar nomination.

Christie made a brief appearance in the third Harry Potter film, Harry Potter and the Prisoner of Azkaban, playing Madam Rosmerta. That same year, she also appeared in two other high-profile films: Wolfgang Petersen's Troy and Marc Forster's Finding Neverland, playing Kate Winslet's mother. The latter performance earned Christie a BAFTA nomination as supporting actress in film.

Christie portrayed the female lead in Away From Her, a film about a long-married Canadian couple coping with the wife's Alzheimer's disease. Based on the Alice Munro short story "The Bear Came Over the Mountain", the movie was the first feature film directed by Christie's sometime co-star, Canadian actress Sarah Polley. She only took the role, she says, as Polley is her friend. On her part, Polley said that Christie liked the script but initially turned it down as she was ambivalent about acting. It took several months of persuasion by Polley before Christie finally accepted the role, which was written with her in mind.