Nicol came up to Pembroke in 1946 as an exhibitioner to read Classics. In 1949 he was awarded the University of Cambridge's Henry Carrington and Bentham Dumont Koe Studentship and the Reginald Taylor Prize Medal by the British Archaeological Association. After being awarded his PhD in 1952, he became Lecturer in Classics at the University College Dublin (1952-1964), after which he spent 2 years as visiting fellow at Dumbarton Oaks, USA, and was then Senior Lecturer and Reader in Byzantine History, University of Edinburgh (1966–1970). In 1970 he was appointed Koraës Professor of Modern Greek and Byzantine History, Language and Literature at King's College London, a post he held until 1988. From 1977-1980 he was Assistant Principal of the King's College, and Vice-Principal in 1980-1981. In 1997 he gave to Pembroke College his library, chiefly of books on Byzantine and later Greek studies. He died in 2003.