In 1956, she was a chorus dancer in the Christmas season of The Adventures of Davy Crockett starring Hermione Baddeley, at the Olympia Theatre, Dublin.

She had a part in the British sex-comedy Confessions of a Pop Performer (1975) and then had a recurring role playing Letty Gaunt in the BBC period drama The Onedin Line (1976–1979).

She became better known in 1980 when she took the lead role in the ITV drama series The Gentle Touch, playing Detective Inspector Maggie Forbes.

This was the first British television drama that centred on a female police officer, coming several months before the BBC's similarly themed Juliet Bravo.

After a high-profile career that had spanned over twenty years on British television, Gascoine and her second husband, actor Alfred Molina, moved to Los Angeles in the 1990s where she made appearances on US television in series such as Northern Exposure and Touched by an Angel, as well as performing extensively in theatre.

Although still living in Los Angeles, she returned to the UK in 2008 to perform at the Edinburgh Festival Fringe in the play Sister Cities at the Gilded Balloon Theatre.

[6] Gascoine suffered from clinical depression for most of her life, which she believed stemmed from her unhappy time in a boarding school as a child.

[5] In 1997, Gascoine was diagnosed with kidney cancer, though the disease was detected early and she made a full recovery.

[7] In August 2016 her husband Alfred Molina reported that she was "in a very advanced stage of Alzheimer's", and had been in a specialist care home in Los Angeles for more than two years, where she died on 28 April 2020, aged 83.