The daughter of British actor John Mills and playwright Mary Hayley Bell, Hayley Catherine Rose Vivien Mills made her first screen appearance as an infant in 1947's So Well Remembered. It wasn't until a decade later, however, that Hayley Mills made her formal film debut, portraying the preteen murder witness who is nearly destroyed by her connection to the criminal in 1959's Tiger Bay. Playing many scenes alongside her own father,Mills gave an uncannily affecting performance that won her the British Film Academy's Most Promising Newcomer Award. The movie also brought her to the attention of Walt Disney, ever on the lookout for talented child actors. In 1959, Mills entered Disney's orbit, and the producer placed her into the most meticulous and artistic live-action film in his studio's history up to that time: Pollyanna (1960). The movie transformed Mills from a precociously talented juvenile player into a full-fledged star, and earned her a special Academy Award for her performance. Ironically, Pollyanna was somewhat mis-marketed at the time as a film intended principally for younger girls and their mothers -- in actuality, it is a sentimental film whose dramatic content and visual craftsmanship place it closer in spirit to pictures like The Music Man, or even Shenandoah, perfectly suitable for general audiences; as a result, it was never as big a hit in theaters as it should have been, and Mills' biggest success for Disney turned out to be her next feature, The Parent Trap (1961). This movie, about a set of estranged identical twin sisters who conspire to get their divorced parents back together, gave the 15-year-old actress the chance to play two separate characters, with two distinctly different personalities. She was able to convince a major part of the audience that she was two different people (a gambit later picked up by the creators of The Patty Duke Show), and she also hit the pop music charts with a song from the film, called "Let's Get Together." In the years that followed, Mills' output for Disney proved somewhat uneven, The Moon-Spinners (1964) failing to impress critics, while the more dramatically demanding The Chalk Garden (1964), in which she played an emotionally crippled adolescent, was some of her best work, and reunited her onscreen with her father; and she excelled in the drama Whistle Down the Wind (1962), directed by Bryan Forbes and made for Rank, playing a girl who shelters an escaped criminal, who thinks he's Jesus.
The advent of the British Invasion in popular music, which imparted an appeal to all things British in America for about two years, helped sustain Mills' popularity, and her final Disney film, That Darn Cat (1965), was a hit and one of her best comedies, though she was outshone (as she might well have been) by old hands like William Demarest. Her first film after leaving the Disney fold was Gypsy Girl (1966), which marked a break from the American producer's tendency toward light comedy -- directed by her father and written by her mother, it presented Mills in the role of a retarded teenager. She was engaged by John and Roy Boulting to star in The Family Way (1966), a comedy about close-quarter familiar relations (best remembered today because of its score, written by Paul McCartney) -- that picture exploded her lingering goody-two-shoes image by offering Mills in a well-publicized nude scene, and what the scene itself didn't accomplish in changing her image, her romance and marriage to director Roy Boulting, some 33 years her senior, did, and the two had a daughter before their divorce in 1976. Mills would also have a lengthy relationship and eventually a son with actor Leigh Lawson.
Curtailing her film appearances in the early '70s, Mills devoted most of her time to television productions; in 1986, she came back to the Disney fold with a Parent Trap TV-movie sequel, and she earned a place in the hearts of a new generation with the title role on 1987's Good Morning, Miss Bliss, the TV precursor to Saved by the Bell. Mills would take a break during the 90's, but returned to TV full force in 2007 with a starring role on the series Wild at Heart.