Award for Best Featured Actress in a Play for her role as Lotte Schoen in the play Lettice and Lovage, in which she appeared in both the London and Broadway productions opposite Dame Maggie Smith. The American Actors' Equity initially refused permission for Tyzack to join the New York production, but Smith refused to appear without Tyzack because of the "onstage chemistry" she believed the two women had created in their roles. In 1994, she played Sybil Birling in the Royal National Theatre production of An Inspector Calls. In 2008, she was acclaimed for her portrayal of Mrs St Maugham in a revival of Enid Bagnold's The Chalk Garden at the Donmar Warehouse, London, for which she won the Best Actress award in the Critics' Circle Theatre Awards and the Olivier award for Best Actress in a Play in 2009. In 2009, she also appeared alongside Helen Mirren in Phedre at the Royal National Theatre. She appeared in two films directed by Stanley Kubrick: 2001: A Space Odyssey (1968) and A Clockwork Orange (1971). Tyzack also appeared in Ring of Spies (1964), The Whisperers (1967), A Touch of Love (1969), The Legacy (1978), The Quatermass Conclusion (1979), Mr. Love (1985), Prick Up Your Ears (1987), The King's Whore (1990), Mrs Dalloway (1997), Bright Young Things (2003), and the Woody Allen films Match Point (2005) and Scoop (2006). However, it was as a television actress that Tyzack became a household name. She is remembered for her leading roles in BBC television productions. She came to notice as Winifred, Soames's sister, in the well received BBC adaptation of Galsworthy's The Forsyte Saga in 1967, a series shown internationally. She portrayed the character of Gladys King in Dennis Potter's The Bone Grinder (1968), a metaphor for the decline of the British Empire and rise of American power in the post-war world. Tyzack played Queen Anne in The First Churchills; Bette in Cousin Bette; and Antonia, mother of the Emperor Claudius, in I, Claudius. She also played Clotilde Bradbury-Scott in the BBC adaptation of the Agatha Christie story Nemesis in 1987 in Miss Marple. In the 1990s, she played a major role in The Young Indiana Jones Chronicles television series as the young Indiana Jones' strict Oxford-educated tutor, Miss Helen Seymour. In the 2000s, she made two appearances in Midsomer Murders. In 2011, she joined the cast of soap opera EastEnders, playing Lydia Simmonds.