Dean was educated at Sherborne School and he attended with first-class honours the School of Natural Science at New College, Oxford, to be graduated MB BCh in 1904, after medical training at St Thomas' Hospital, where he was medical registrar and after resident assistant physician.

After a senior demyship at Magdalen College, Oxford, he took MRCP in 1906, a Radcliffe Travelling Fellowship in 1909 (to study at Wassermann Laboratory, Berlin), D.M.

[1] From 1910 he was assistant bacteriologist at the Lister Institute, London before to become in 1912 Professor of Pathology and Bacteriology at the University of Sheffield.

[1][3] Dean was engaged to design a new building of the Department of Pathology in Tennis Court Road, where it is today from September 1928.

[1][4] In 1946 he improved his course (58 lectures) with a training scheme for the would-be pathologists (2 or 3 years of experience of laboratory work).