Born in Chelsea, London, the daughter of Sydney Earnshaw Greenwood (1887–1949), a portrait Artist, and Ida Greenwood (née Waller), Joan Greenwood studied at the Royal Academy of Dramatic Art and worked mainly on the stage, where she had a long career, appearing with Donald Wolfit's theatre company in the years following the Second World War.
Greenwood made several memorable screen appearances just after the war, in Ealing Comedies, in Whisky Galore!; as the seductive Sibella in the black comedy Kind Hearts and Coronets (1949); and in The Man in the White Suit (1951). She opened The Grass is Greener in the West End in 1952, and played Gwendolyn in a film version of The Importance of Being Earnest released in the same year.
She had a leading role in Stage Struck (1958), an adaptation of Jules Verne's Mysterious Island (1961), and was nominated for the Golden Globe for Best Supporting Actress for Tom Jones (1963).
In 1960 Greenwood appeared as the title character in a production of Hedda Gabler at the Playhouse, Oxford. Starring opposite her as Judge Brack was the actor André Morell. They fell in love and flew in secret to Jamaica, where they were married, remaining together until his death in 1978.
Greenwood appeared as Olga, alongside Spike Milligan in Frank Dunlop's production of the play Oblomov, based on the novel by Russian Writer Ivan Goncharov. The play opened at London's Lyric Theatre on 6 October 1964. Greenwood was described as "a model of generosity and tolerance ... the only person in the cast who could not be 'corpsed' by Milligan; although he tried very hard. She looked beautiful, and played the part of Oblomov's unfortunate lady with total integrity. 'She never left the script', says Milligan with a guilty smile of something between irritation and admiration. 'I just couldn't make her crack up. All the rest of us did. She never lost her dignity for a moment.'"
Joan Greenwood died of a heart attack in London, less than a week before her 66th birthday. With her husband she had one child, Jason Morell, a film actor who appeared in Mrs Brown (1997, as Lord Stanley), and Wilde (also 1997, as Ernest Dowson).
