Born Hayley Catherine Rose Vivien Mills in London in 1946, she is the daughter of the great actor Sir John Mills and the well-known novelist-playwright Mary Hayley Bell. Her sister is the actress Juliet Mills. She grew up in her parents' home, an outgoing, funny child, and, because she spent so much time with her parents and their friends, very intelligent. When she went to boarding school at age nine, however, she became very shy around kids her own age. She found solace in theater productions at her school. She was noticed playing at her parent's home in 1958 by director J. Lee Thompson, who immediately cast her opposite her father in the thriller Kohtalokas kotiinpaluu (1959). Her debut performance turned heads around the world, from Germany, where she won an award at the Berlin Film Festival, to Hollywood, when Walt Disney came knocking at her door. He signed her to a five-year contract. For her first film for the studio, Pollyanna - iloinen tyttö (1960), she won critical raves, box-office success, and a special Juvenile Academy Award. Her second Disney film, Ansa vanhemmille (1961), in which she played twins, was even more popular. She continued to appear in routine Disney films like Kapteeni Grantia etsimässä (1962) and Kesän taikaa (1963), as well as films outside the studio like Viattomat (1961), based on her mother's novel, and Kotiopettajattaren salaisuus (1964), again co-starring with her father. Though Disney gave her a somewhat more adult role in the mystery film Vaarojen lahti (1964), she had begun to tire of her sunny, innocent Pollyanna image. After completing Pahuksen katti (1965), she left the studio for good. Pahuksen katti (1965) was still a success, as was her first post-Disney film, Columbia's Harmia enkeleistä (1966). Then, she shocked her fans by appearing in the comedy Kuherruskuukausi (1966) with her father. There was an even bigger surprise in store when she fell in love with the film's director, Roy Boulting, who was 33 years her senior. She lived with Boulting for five years after he divorced his wife. They married in 1971 and had a son, Crispian Mills, in 1973. By this time, he'd taken control of her career, and, as a result, she made many bad film choices that left critics and audiences cold. By 1975, her film career had pretty much tanked. She separated from Boulting that year and moved in with actor Leigh Lawson, with whom she had a son, Jason, in 1976. They split up in 1984. She appeared in three TV-movie sequels to Ansa vanhemmille (1961) in the 1980s, and also appeared in the BBC miniseries The Flame Trees of Thika (1981) and the TV series Good Morning, Miss Bliss (1987), later re-titled Saved by the Bell (1989). She hasn't done much film work in several years, preferring to concentrate on her burgeoning career in theater. Her greatest success in theater, so far, has been the role of Anna in "The King and I", which she has played in many touring stage productions throughout the 1990s.