Born Dorothy Isobel Cox in London, England, she was a successful British stage actress of some elegance and beauty. In her day she was reckoned the equal in the theatre of more famous names such as Peggy Ashcroft and Celia Johnson. As a film actress in a major role, such as "Gaslight" she could be luminous and powerful.

After success in Liverpool and London she attracted attention on Broadway and appeared first in Rasputin and the Empress in 1932, with Ethel, John, and Lionel Barrymore. Fox then borrowed her for their lavish version of Noel Coward's stage spectacle "Cavalcade", and she became the first British actress to be nominated for the Best Actress Oscar. As the noble wife and mother she aged gracefully against a background of the Boer War, the sinking of the Titanic, the First World War, and the arrival of the Jazz Age.

After a brief and largely unsatisfactory Hollywood career, most notably as John Barrymore's old flame in "Reunion in Vienna", she returned to Britain. Here she concentrated on theatre work, including roles as Charlotte Bronte in Clemence Dane's "Wild Decembers", in "Sweet Aloes", and as Gilda in the British premiere of Noel Coward's "Design for Living."

Tempted to return to the screen to play opposite Ralph Richardson in "On the Night of the Fire" she had a great success as the frightened heroine of the first film version of Patrick Hamilton's play "Gaslight" in 1939. This led to infrequent prestigious appearances on the screen, including roles opposite Clive Brook in "Freedom Radio", John Gielgud in "The Prime Minister" and Michael Redgrave in "Kipps", directed by her then husband Carol Reed. After the War she enhanced the Technicolor elegance of Alexander Korda's "An Ideal Husband", as the wife in question, but her remaining film roles were small, usually providing graceful maternal support in roles in the 1950s such as "Tom Brown's Schooldays" and as the secretive mother, incredibly, of James Mason, in "Island in the Sun." On television she played the Empress Elizabeth of Austria in the Audrey Hepburn version of "Mayerling."

Her stage career, however, flourished after the War, and as a Shakespearian leading lady at Stratford, in London's West End, and on tour in Australia, she had her pick of star parts. Between 1948 and 1952 she memorably played Portia, Gertrude,Lady Macbeth, Katherine the shrew, Desdemona, Katherine of Aragon, Hermione in "The Winter's Tale", and perhaps most notably Beatrice to Gielgud's Benedick in "Much Ado About Nothing." In this production she succeeded her friend Peggy Ashcroft. She famously stumbled off the rostrum during the sleepwalking scene in Macbeth in 1948 and fell 15 feet - and continued.

Throughout the 1940s and 1950s she also had success in the works of several contemporary writers, including the British production of Tennessee Williams' "Camino Real." She died from renal disease in London,in 1964 aged 58, while rehearsing "The Master Builder" with Michael Redgrave and Maggie Smith as part of the new National Theatre company. Celia Johnson replaced her.

She was married to the English film director Sir Carol Reed from 3 February 1943 until August, 1947, and subsequently to the physician Tibor Csato. .