In 1910 he joined the Department of Printed Books of the British Museum.
In 1909 and 1914, showing his interest in Roman history, he published two books on the subject.
During the First World War, worked for the Postal Censorship Bureau. At the close of hostilities he returned to his work at the British Museum and his attention carried him towards the study of antique coins.
He also translated Tacitus' works Agricola and Germania. These two translations were published together in 1948 by Penguin Books under the title Tacitus on Britain and Germany.[5] 27,000 copies of this book were sold in that year.[6] It was reprinted in 1951, 1954,[7] 1960, 1962, 1964 and 1965.[8] The second edition, revised by S A Handford, was published in 1970 under the title The Agricola and the Germania. The book was revised again in 2009 by J B Rives.[9] Mattingly's translation is considered one of the best[by whom?] and is still used (albeit in edited format) today.
Outlines of Ancient History, from the earliest times to the fall of the Roman Empire in the West, A.D. 476. Cambridge: Cambridge University Press, 1914.
Coins of the Roman Empire in the British Museum, 6 volumes. London: British Museum, 1923-1963.
^Harold Mattingly and Cornelius Tacitus. Tacitus on Britain and Germany. Penguin Books. 1948. Google Books.
^Jeremy Munday, Evaluation in Translation: Critical Points of Translator Decision-making, Routledge, 2012, p 105
^Harold Mattingly and Cornelius Tacitus. Tacitus on Britain and Germany. Penguin Books. 1948. Reprinted 1954.
Google Books
^Harold Mattingly and Cornelius Tacitus. Tacitus on Britain and Germany. Penguin Books. 1948. Reprinted 1965. Google Books.
^For reviews of, and other commentary on the various editions of this book, see (1971) 1-3 American Classical Review 158 [1]; (1950) 33 Saturday Review of Literature 46 [2][3]; (1949) 81 Journal of Education 686 [4][5]; D M Loades, Readers Guide to British History, Fitzroy Dearborn, 2003, vol 2, p 1136 [6]; (1968) Arion, p 473 [7]; (1948) 89-100 British Book News 690 [8]; Tacitus: Oxford Bibliographies Online Research Guide, OUP, 2010, p 14