King's father, William Albert de Courcy King, was born in 1875. He married Georgina Marie, daughter of a "Mr. D. F. MacKenzie, of Collingwood Grange, Camberley, Surrey" in June 1908. De Courcy King attended Royal Military Academy, Woolwich and then the School of Military Engineering, Chatham. He received his commission as a second lieutenant in the Royal Engineers in 1894. Prior to World War I, his postings included Saint Lucia in the 1890s, where the Engineers constructed gun emplacements and fortified coal stations, and South Africa, where the Engineers built blockhouses (designed by Major S. R. Rice, RE) during the Anglo Boer War. De Courcy King was awarded the Distinguished Service Order (DSO) in 1916 while a major, during the First World War, serving later as Lieutenant-Colonel with the 36th (Ulster) Division in Belgium. He was killed on 27 May 1917 at the age of 42, and lies buried at Dranoutre Military Cemetery in Belgium.