Smith excelled in both comedy and drama performing in various works of Shakespeare, Anton Chekhov, Noël Coward, Edward Albee and Tom Stoppard.
Other notable roles include Travels with My Aunt (1972), Death on the Nile (1978), A Room with a View (1986), Richard III (1995), Gosford Park (2001) and Quartet (2012).
Smith also starred in the commercially successful films Hook (1991), Sister Act (1992), The Secret Garden (1993) and The Best Exotic Marigold Hotel (2011) and its sequel.
Smith received Primetime Emmy Award nominations for her work in Suddenly, Last Summer (1992), David Copperfield (1999) and Capturing Mary (2010).
Smith gained international acclaim for her performance in Downton Abbey (2010–2015) as the Violet Crawley, Dowager Countess of Grantham.