After a couple of roles in Broadway productions during the 1930s, Dunnock won praise for her performance as a Welsh school Teacher in The Corn is Green in 1940. The 1945 film version marked her screen debut. During the 1940s she performed mainly on stage, in such dramas as Another Part of the Forest (1946) and Death of a Salesman (1949) and in the musical Lute Song (1946). In 1947, Dunnock became a founding member of the Actors Studio.