In 1934 he took his MA at Manchester, writing on Droplaugarsona saga, and then spent a further year there gaining a teaching certificate.
During these years, he continued to spend much of his time in Iceland, meeting his future wife Sigríður Ásgeirsdóttir (1911–91) there in 1935.
Arnold continued both to fight and translate in North Africa, Italy, Belgium and the Netherlands until the summer of 1946, when he returned to high-school teaching in County Durham.
In January 1947 Arnold began the career which dominated his life, gaining a lectureship in the English Department at the University of Leeds, where he succeeded Bruce Dickins (who had himself succeeded Arnold's tutor E. V. Gordon when Gordon left Leeds for Manchester) in teaching medieval English, Old Norse and modern Icelandic Studies.
He also produced an Icelandic-English Pocket Dictionary (Reykjavík: Orðabókarútgáfan, 1956) and a number of articles, though ill health hampered his writing.