Nicol was born in
Portsmouth,
Hampshire, to a
Church of Scotland minister, and received a classical education at
King Edward VII School in
Sheffield and
St Paul's School in
London. Registering as a
conscientious objector in 1941, he served in 1942–1946 in the
Friends' Ambulance Unit, with which he first visited
Greece in 1944–1945, visiting
Ioannina and the
Meteora monasteries. After his wartime experiences, Nicol matriculated at
Pembroke College, Cambridge, to read classics, graduating in 1949. He then returned to Greece in 1949–1950 as a member of the
British School at Athens. During this time, he also visited
Mount Athos, spending
Easter 1949 at the
Hilandar Monastery, and revisited Meteora. In 1950, Nicol married Joan Mary Campbell, with whom he had three sons. He completed his doctoral thesis at Cambridge in 1952. The thesis, on the medieval
Despotate of Epirus, led to his first book,
The Despotate of Epiros. His thesis supervisor was
Steven Runciman, with whom Nicol formed a lifelong friendship, nurtured in the
Athenaeum Club. On completion of his doctorate, Nicol's first academic posting was as Lecturer in Classics at the
University College Dublin from 1952 to 1964. He spent 1964–1966 as visiting fellow at
Dumbarton Oaks, and was then Senior Lecturer and Reader in Byzantine History,
University of Edinburgh (1966–1970). In 1970 he was named to the historic chair of
Koraës Professor of Modern Greek and Byzantine History, Language and Literature at the
King's College London, a post he held until 1988. In 1977–1980 he was Assistant Principal of the King's College, and Vice-Principal in 1980–1981. He was the founding editor of
Byzantine and Modern Greek Studies journal (1975), whose publication he oversaw until 1983, and served as president of the Ecclesiastical History Society in 1975–1976. In 1989–1992, he was director of the
Gennadius Library (Γεννάδειος Βιβλιοθήκη) in
Athens. Nicol became a member of the
Royal Irish Academy in 1960, President of the
Ecclesiastical History Society (1975-76) and a Fellow of the
British Academy in 1981. For his contributions to the history of medieval
Epirus, the city of
Arta made him an honorary citizen in 1990, and he was awarded an honorary doctorate by the
University of Ioannina in 1997. He died in
Cambridge in 2003. ==Works==