Patty Duke, who has died of complications from a ruptured intestine aged 69, was one of the few actors whose career, covering several decades, could be said to have peaked at its beginning – with her demanding role as Helen Keller, the deaf, blind and speech-impaired six-year-old, in The Miracle Worker, both on stage (1959) and on screen (1962). There were other highs, including her own television sitcom, but Keller was a role that could only come once in a lifetime.

The play, by William Gibson, which opened at the Playhouse theatre on Broadway in 1959 and was directed by Arthur Penn, was a fascinating study of how Annie Sullivan (Anne Bancroft), a young teacher, struggles to "disinter the soul" of her disabled pupil, gradually giving her the ability to communicate. During physical tussles with her teacher, Keller, played movingly by the 12-year-old Duke, often groans, flailing her arms in an attempt to reach something she cannot clearly identify. One scene in particular, of the teacher trying to tame the young girl's tantrums, is an indelible theatrical tour de force. The film version, with the same cast and director, offered a vivid record of the stage performances of Bancroft and Duke, both of whom won Academy Awards, the latter becoming, at 16, the youngest Oscar winner to date. Initially United Artists were against casting Bancroft (not well-known enough) and Duke (too old to play a six-year-old), but Penn insisted. His determination paid off, and brought fame to all concerned.

Although this was a peak reached incredibly early, it would be grossly unfair to say that it was downhill all the way for Duke from then on. Soon after receiving the Oscar, she had a success on television with The Patty Duke Show (1963-66), a carefree sitcom in which she had a chance to demonstrate her versatility playing identical but contrasting cousins, Patty Lane, a chatty, rather bubble-headed American teenager, and Cathy Lane, brainy and demure, from Scotland. As the catchy theme song had it: "Where Cathy adores the minuet, the Ballets Russes and crepes Suzette, our Patty loves to rock'n'roll, a hot dog makes her lose control."

She was born Anna Duke in Queens, New York, the youngest of three children of Frances (nee McMahon), a cashier, and John, a handyman and taxi driver. Her father was an alcoholic, and her mother suffered from clinical depression. When Anna was eight, she was fostered out to the talent agents John and Ethel Ross, who got her into showbusiness but exploited her shamelessly, taking most of the child's fees for themselves, giving her alcohol and painkillers and, as was revealed in Duke's 1987 autobiography, Call Me Anna, sexually abusing her.

It was they who trained her for the role of Helen Keller by keeping her blindfolded for considerable lengths of time and creeping up on her with loud sounds, such as banging on a bucket, until she failed to react to them.

As a child actor, Duke had substantial roles in TV movie versions of Swiss Family Robinson (1958), Meet Me in St Louis (1959) and The Power and the Glory (1961), the last starring Laurence Olivier as Graham Greene's "whiskey priest". On the big screen she played opposite Kim Stanley as an unloved child in The Goddess (1958), and as TV-hating David Niven's daughter in Happy Anniversary (1959). She shone as an ebullient teenager in Billie (1965), a proto-feminist comedy in which she is a tomboy – cropped hair is the signifier – who runs faster than the boys in college athletics.

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At 18, Duke married the director Harry Falk, mainly in an effort to free herself from the Rosses. In 1967, shocking many fans of her family-oriented sitcom, she took a starring role in the sensationalist Valley of the Dolls. In it she pulled out all stops in her portrayal of Neely O'Hara, a brash film star who falls victim to the eponymous "dolls" (slang for the drug Dolophine), betrays her husband and is committed to a sanatorium for rehabilitation. Duke then gathered all the good reviews in the title role of Me, Natalie (1969), in which she leads a Bohemian existence in Greenwich Village, meeting, among others, Al Pacino, making his screen debut as a gigolo.

She spent most of the 1970s appearing on television, and received three Emmys. Her first was for My Sweet Charlie (1970), in which she was a pregnant teenager on the run. Because her acceptance speech was rambling and incoherent, many believed her to be drunk or stoned. In fact, she was suffering from the beginnings of a bipolar disorder, which was diagnosed only in 1982, when Duke made it public.

However, the condition did not prevent her from continuing her acting career, mostly on television, or from becoming president of the Screen Actors Guild from 1985 to 1988. Among the several TV series she made was Hail to the Chief (1985), in which she portrayed the first female American president. According to Duke, the series failed, despite good reviews, because "viewers couldn't accept the idea of a woman president".

She returned to the Broadway stage in 2002 as Aunt Eller in a revival of Oklahoma! and, coming full circle, directed The Miracle Worker at a theatre in Spokane, Washington, in 2011. But most of her activities were connected with educating the public on bipolar disorder, lobbying Congress, and working with the National Institute of Mental Health and National Alliance on Mental Illness to increase awareness and funding.

Duke is survived by her fourth husband, Michael Pearce, and their son Kevin, by two sons, Sean and Mackenzie, from previous relationships, and by six grandchildren.

• Patty (Anna Marie) Duke, actor, born 14 December 1946; died 29 March 2016

Ronald BERGAN
first published in:
www.theguardian.com/stage/2016/apr/01/patty-duke-obituary