Fletcher was born on 24 April 1941. His parents were Dr. (Clarence) John Molyneux Fletcher (younger brother of
Eric Fletcher, Baron Fletcher) and Isabel Chenevix Trench. His maternal grandfather Reginald Chenevix Trench, who died in the Great War, had a sister
Cesca, a
Sinn Féin supporter who was at the
General Post Office, Dublin during the
Easter Rising of 1916. Isabel Fletcher was born in November 1915, shortly before her father's death. Fletcher produced a series of recordings about his Irish forebears for the Irish Life and Lore website. After government service as a research metallurgist at
Harwell, he became an antiquarian who pioneered the use of
dendrochronology in the Research Laboratory for Archaeology and the History of Art at the
University of Oxford, dating medieval buildings, structures, and paintings on panel. Fletcher was educated at
Wellington College from 1954 to 1959, where he was an avid historian, journalist and stamp collector. In spite of his talent, he failed History at O-Level, which he considered "unpassable". On leaving school, he read history from 1959 at
Merton College, Oxford, where he was a contemporary of
R. I. Moore. At Oxford, he was particularly influenced by
W. G. Hoskins.
J. P. Kenyon called Fletcher's
The Outbreak of the English Civil War "easily the most important book on the Great Rebellion in the past 20 years". Fletcher's
festschrift was published in 2007 by the Cambridge University Press (
The Family in Early Modern England, edited by
H Berry and E Foyster). Fletcher died on 3 January 2026, at the age of 84. ==Works==