Josephson spent a postdoctoral year in the United States (1965–1966) as research assistant professor at the University of Illinois at Urbana–Champaign. After returning to Cambridge, he was made assistant director of research at the Cavendish Laboratory in 1967, where he remained a member of the Theory of Condensed Matter group, a theoretical physics group, for the rest of his career. He was elected a Fellow of the Royal Society (FRS) in 1970, and the same year was awarded a National Science Foundation fellowship by Cornell University, where he spent one year. In 1972 he became a reader in physics at Cambridge and in 1974 a full professor, a position he held until he retired in 2007.