In 1922 when R.E. Mortimer Wheeler, Keeper of the department of archaeology of the National Museum of Wales, Cardiff, was made Director of the museum, his former post became vacant. Although there was pressure to appoint an archaeologist with a Welsh background, Wheeler recommended Fox for the post and he was appointed. When Wheeler left in 1926 to take up a post in London, Fox was appointed in his place as Director of the National Museum of Wales.
During his time as Director, Fox continued to work in the field of archaeology and the Museum published several of his works, amongst them The personality of Britain (1932), A find of the early Iron Age, Anglesey (1946) and (with Lord Raglan) Monmouthshire houses (1951-54). He also surveyed Offa's Dyke, the results of which were published in issues of Arch. Camb. After his retirement the Museum published his Pattern and purpose: a study of early Celtic art in Britain (1958). He received many honours; amongst them, knighthood (1935), F.B.A. (1940), G.T. Clarke award (1946), president (1944-49) of the Society of Antiquarians of London and its gold medal (1952), honorary D.Litt. University of Wales (1947), president of the Museums Association (1933-34), president of the Cambrian Archaeological Society (1933), honorary fellow of Magdalene College, Cambridge (1953).
He married twice: (1) Olive Congreve-Pridgeon (d. 1932), they had two daughters; (2) Aileen Mary Scott-Henderson, they had three sons. After retiring, he lived in Exeter and died there 16 Jan. 1967.
Iorwerth Cyfeiliog Peate, D.Sc., F.S.A., D.Litt., (1901-82), St Fagans / Llandaf