William was educated at Royal High School, and at Edinburgh University, qualifying M.B., Ch.B. in 1904, and D.T.M. and H. in 1910. He joined the Medical Staff Corps (V) in 1899, serving with them until 1902. On 30th July 1906 he took up a commission at the rank of Lieutenant in the R.A.M.C. He served in the South Africa from 1907 to 1912, during which time he gained promotion to the rank of Captain on 30th January 1910. William was serving with the Irish Command when war broke out. He was mobilized for war on the 4th August 1914, joining the 1st Field Ambulance the following day at 2 p.m. at Aldershot. He entered the war in France with the unit on the 18th August 1914. On 11th November the Officer Commanding of the unit received correspondence from the A.D.M.S. He wrote:- “Ordered to send an RAMC officer to RE Divnl Head Qtr to replace Capt IRVINE, RAMC, who is to join this unit. I have only two Captains RAMC available for this duty, one is Adjutant to the Unit, the other Transport Officer & Commanding a Section. I am sending Capt FORSYTH who has been doing the duties of Adjutant & who has been invaluable in that capacity to me. He will be very hard to replace, owing to his knowledge of drill, corps duties, etc.” William appears to have served with the 12th Field Ambulance during March - August 1915, then with the 47th Field Ambulance during 1915-1916. On the 12th April 1916 he began to serve under the rank of temporary Major, then from 22nd August 1916 to 17th October 1919 under the rank of acting Lieutenant Colonel. He was granted the rank of Major on 30th July 1918. From March 1916 to 1919 he was the Commanding Officer of the 38th Field Ambulance. At some point William also appears to have served with No 15 Casualty Clearing Station. After the war he went to India, serving there from 1920 - 1923. William was the husband of Maisie Prentice.