Jo Botting, a British Film Institute curator and friend, said Harris died Saturday at a London hospital after suffering from a chest infection.
Harris played a major role in capturing the look of 1960s "Swinging London" on film. She dressed The Beatles for both "A Hard Day's Night" and "Help!" — saying later, "I must be one of the few people who can claim they have seen John, Paul, George and Ringo naked."
She won an Oscar for "Darling," a style-setting film about London models and media types starring Dirk Bogarde and Julie Christie, and a British film award, the BAFTA, for the 1966 Michael Caine comedy "The Wrong Box."
Harris worked on the James Bond spoof "Casino Royale" in 1967, and created costumes for Roger Moore's first outing as 007, "Live and Let Die," in 1973. She designed for a vampiric Frank Langella in a 1979 version of "Dracula," and for "The Great Muppet Caper" (1981).
Harris is survived by her goddaughter, Serena Dilnot.