He started his military career as a private in the 8th Regiment, Royal Rifles. He was promoted to lieutenant and then to captain in 1903, major in 1910, and lieutenant-colonel in 1912. In 1914, he enlisted in the Canadian Expeditionary Force and was soon given command of the 2nd Battalion, CEF. He was promoted to Brigadier-General in 1915 and took command of the 5th Brigade, 2nd Canadian Division. He was promoted to Major-General and took command of the 4th Canadian Division upon its creation in 1916. He led his various commands in most of the major Canadian battles of World War I including Second Ypres, the Somme, Vimy Ridge, Passchendaele, Amiens, Second Arras, and Cambrai.