William was educated at Glasgow University, where he took the M.B. and C.M. in 1893. He entered the R.A.M.C. at the rank of Surgeon-Lieutenant on 29th January 1895, then served in the Tirah campaign on the North West Frontier of India in 1897 - 1898, receiving the medal with two clasps. On 29th January 1898 he became Surgeon-Captain, then Major on 29th July 1906, Brevet Lieutenant-Colonel on 4th July 1914 and Lieutenant-Colonel on 1st March 1915. From 1st February 1906 to 21st August 1909 he was Assistant Professor of Medicine at the R.A.M. College, Millbank. Then became Professor of Medicine at the R.A.M. College from 22nd August 1909 to 21st August 1913. After that he became Senior Medical Officer in Jamaica. William died at Haslingden, Lancashire. He was the son of Jonathan Harrison, M.D., J.P., and Margaret Harrison of Haslingden; and the husband of Edith Harrison (nee Bennell) of 126 Ashbourne Road, Mitcham, Surrey.