Jones was a native of New Tredegar, Monmouthshire. His translations include Four Icelandic Sagas (1935), The Vatndalers' Saga (1944), The Mabinogion (1948) (in collaboration with Thomas Jones), Egil's Saga (1960), Eirik the Red and Other Icelandic Sagas (1961) and The Norse Atlantic Saga (1964). He also wrote A History of the Vikings (1968) and Kings, Beasts and Heroes (1972). In honor of his scholarship, Jones received the Commander's Cross of the Order of the Falcon from the President of Iceland in 1963.
In addition to his translations, he was an author in the Anglo-Welsh tradition. His novels and story collections include Richard Savage (1935), Times Like These (1936), The Nine Days' Wonder (1937) and Garland of Hays (1938), The Buttercup Field (1945), The Flowers beneath the Scythe (1952), Shepherd's Hey (1953) and The Walk Home (1962).
Jones also founded The Welsh Review in 1939, which he edited until 1948; this journal was important for raising discussion of Welsh issues and for attracting submissions from such authors as T. S. Eliot and J. R. R. Tolkien. He continued to support Welsh literature by chairing both the Welsh Committee of the Arts Council of Great Britain and the first editorial board of The Oxford Companion to the Literature of Wales. He also published three sets of lectures on Anglo-Welsh literature: The First Forty Years (1957), Being and Belonging (1977), and Babel and the Dragon's Tongue (1981).