Larkin began teaching art history at Smith College from 1924. He was inclined to teach on account of his father and encouraged by his art teachers at Harvard. He was an associate professor by 1926, and in 1931 a full professor. He briefly also taught at Iowa State University in 1925 and 1926. He was later named Jessie Wells Post Professor of Art. In 1950 and 1955 Larkin lectured for European students at the Harvard Student Council's seminars on American studies in Salzburg. He retired from Smith College in 1964, as professor emeritus.