Griffiths was born and brought up in a mining valley between Glamorgan and Monmouthshire.[1] He attended "one of Wales' good grammar schools and was well taught in most subjects".[1] He is a graduate of the University of Bristol and was appointed to a research post, and then promoted to higher academic positions, at Swansea in 1964.[2]
Sir Rhys ap Thomas and his Family: A Study in the Wars of the Roses and Early Tudor Politics, 2nd edn, with a new introduction, University of Wales Press, 2014. ISBN9781783160143
(ed. with Peter Wakelin), Hidden Histories: Discovering the Heritage of Wales (Aberystwyth: Royal Commission on the Ancient and Historical Monuments of Wales, 2008)
(with Roger S. Thomas) The making of the Tudor dynasty, 3rd edn. (Stroud: Sutton, 2005)
(ed.), The Household Book (1510–51) of Sir Edward Don: An Anglo-Welsh Knight and his Circle (Bedford: Buckinghamshire Record Society, 2004)
The Short Oxford History of the British Isles: The Fourteenth and Fifteenth Centuries (Oxford: Oxford University Press, 2003)