 Following his education at Malvern College, Guy was commissioned a second lieutenant in the Worcestershire Regiment on 16 February 1898, and promoted to lieutenant on 10 January 1900.In October 1901 he was seconded for service in South Africa, during the Second Boer War.He later served in the First World War as an acting lieutenant-colonel commanding the 1st, 2nd and 3rd battalions of the regiment, receiving the Distinguished Service Order (DSO) and bar in 1918 for conspicuous gallantry and leadership in the field.