John received his medical education at Trinity College, Dublin, qualifying B.A., M.B. in 1885. He joined the Army Medical Services on 28th July 1886 at the rank of Captain, and gained promotion to the rank of Major on 28th July 1898. He served in South Africa from 1899 to 1902. On 28th July 1906 he was promoted to the rank of Lieutenant Colonel. At the outbreak of war he was stationed at Salisbury. After being mobilized he formed No 5 General Hospital and became the unit Commanding Officer. He entered war in France on 19th August 1914. On 5th October 1914 he succeeded Col Barefoot as the Assistant Director of Medical Service (A.D.M.S.) of Advanced Base. The Advanced Base moved from Le Mans to Abberville on 9th December 1914. On 1st March 1915 he gained further promotion to the rank of Colonel. He was appointed Companion Order of the Bath (mil.) on 14th January 1916. On 7th February 1918 he gained promotion to the rank of Major-General.