Jenkins studied Classics at school, and then went to Greece as a student in the British School at Athens, from 1933 to 1936. There he served as assistant director, and since 1936 as a member of the Board of the Managing Committee; 1948 he was named a trustee, and from 1951 to 1958 he served as Chairman of the Managing Committee. From 1936 to 1946 he was Lewis Gibson Lecturer in Modern Greek at the University of Cambridge. During World War II he served with the British Foreign Service. In 1946 he was appointed Koraes Professor of Modern Greek and Byzantine History, Language and Literature at King’s College London, as well as Honorary Lecturer in Classical Archaeology. Since 1960 until his death he was Professor of Byzantine History and Literature at the Dumbarton Oaks institute.
Constantine Porphyrogenitus: De Administrando Imperio. Ed. Gyula Moravcsik, transl. Romilly James Heald Jenkins. Budapest 1949; 2nd Ed., Washington, DC, 1968, reprinted 2008, ISBN 0-88402-343-5. Croatian edition: Konstantin Porfirogenet, O upravljanju carstvom, prijevod i komentari Nikola pl. Tomašić (hrvatski), R. [Romilly] J. [James] H. [Heald] Jenkins (engleski), priređivač grčkog izvornika Gyula Moravcsik, Zagreb: Dom i svijet (Biblioteka Povjesnica), 2003. ISBN 953-6491-90-7.
Studies on Byzantine history of the 9th and 10th centuries. Variorum Reprints, London, 1970, ISBN 0-902089-07-2.