Evans made her professional debut in 1912 as Cressida in Shakespeare's Troilus and Cressida, directed by William Poel. Preferring interesting and difficult portrayals to starring roles, she turned down the lead in Somerset Maugham's Our Betters in 1923 for a minor part in George Bernard Shaw's Back to Methuselah. In 1925 she joined the Old Vic theatre company, with which she continued to act for many years.

In her long career Evans acted in a variety of parts and produced a number of plays. Some of her more notable stage roles included Judith Bliss in Noel Coward's Hay Fever; Mrs. Millamant in William Congreve's Way of the World; the Countess in The Dark Is Light Enough, which Christopher Fry wrote for her; Gertrude in Hamlet; the nurse in Romeo and Juliet; and, her most famous role, Lady Bracknell in Oscar Wilde's The Importance of Being Earnest. Her last stage performance was in a one-woman show in 1974. Her memorable films include The Importance of Being Earnest (1952), Look Back in Anger (1959), The Nun's Story (1959), Tom Jones (1963), The Chalk Garden (1964), Young Cassidy (1965), The Whisperers (1967), and Crooks and Coronets (1969). She was made a Dame of the British Empire in 1946.