Shortly after the First World War began in August 1914, he was dispatched along with his battalion to England, where it became part of the 21st Brigade of the 7th Division, soon after the outbreak of war. The battalion arrived on the Western Front in October where it fought in the First Battle of Ypres and sustained very heavy casualties. Clutterbuck was promoted to the temporary rank of lieutenant on 31 October 1914 (made permanent in January 1915), and promoted to captain 20 March 1916. From 15 October 1915 he served as adjutant to the 1/10th Battalion, London Regiment, part of the 162nd (East Midland) Brigade of the 54th (East Anglian) Division, in Gallipoli, Egypt and Palestine later becoming adjutant of the Suffolk Yeomanry, and finally becoming a brigade major with the 232nd Brigade. He ended the war having been awarded the Military Cross (with Bar), the Order of the Crown of Italy, was twice wounded in action and was mentioned in dispatches. His older brother, David Clutterbuck, a lieutenant in the Royal Field Artillery, was killed in action in May 1917. In October 1919, after serving in Russia during the Russian Civil War, he married Gwendolin Atterbury Younger; they had one son and two daughters; Rosemary Imogen Atterbury, Michael Edmund Henry, born on 22 July 1920, and Ann Hope Madaline, born on 24 September 1922.