Between 1931 and 1935, Smalley taught at Royal Holloway College, when she left to become a research fellow at
Girton College, Cambridge. Later, she was a temporary assistant in Western manuscripts at the Bodleian Library, Oxford, and, in 1944, became tutor in history at St Hilda's College. Smalley remained in that position until 1969, while from 1957 onwards she was also the college's
Vice-Principal. One of her more notable pupils was the internationally respected historian on mid-Tudor England, Jennifer Loach, a tutorial fellow at
Somerville College, Oxford. Smalley discovered the lost biblical lectures of
John Wycliffe, though she had no sympathy for the man himself. According to
R. W. Southern, she "could not tolerate his stridency and his putting the Bible above the Church." Smalley was a member of the Marxist Historians Group until 1956, when most members of the group left. Later she delivered the
Ford Lectures on
Thomas Becket. ==Honours==