Arnold was educated at Haileybury; at New College, Oxford; and at the London Hospital, where he graduated M.B., B.Ch. (Welsh Prize Human Anatomy 1909) in 1914. He was appointed House Surgeon at the Poplar Hospital, where he worked until February 1915. He obtained a commission as Lieutenant in the R.A.M.C. (T.F.) on 28th April 1915, then entered the war in Gallipoli on 7th June 1915. He was promoted to Captain in the October the same year. He was killed by shell fire. He was the fourth son of Arthur (a tea and Colonial broker) and Alice Elizabeth Thompson of Garthlands, Reigate Heath, Surrey.