The fifth son of Hugh, third Earl Fortescue, by his wife, Georgiana, John William Fortescue was brought up at Castle Hill, the family seat at Filleigh. He was educated at Harrow and Trinity College, Cambridge, in 1878, leaving to read law. In 1880 he became private secretary to Sir William Robinson, governor of the Windward Islands. He returned to complete his degree at Cambridge, and then spent four years in New Zealand as private secretary to the governor, Sir William Jervois, during which he began writing. He was best known for this multivolume history of the British Army, which was published in thirteen volumes between 1899 and 1930.