[1] Jenkins was born in Blaenclydach, Rhondda the son of an Aberaeron-born collier but, as a consequence of illness, spent most of his childhood with an aunt and uncle in Penrhyn-coch, Aberystwyth, Ceredigion.
Conscripted into the Army, he served during World War II as a major in north-western Europe, "taking part in the liberation of Paris and the push into Germany and Poland, where he was among the first British soldiers to reach the concentration camps".
[1] He resumed his career at the National Library, becoming an Assistant Keeper in the Department of Printed Books from 1949 to 1957.
He served as the General Commissioner of Income Tax 1968–1987 and the chairman of the Welsh Books Council from 1974 to 1980.
His history of the National Library, A Refuge in Peace and War, was written over a 20-year period.