John William Fortescue was born in Madeira on 28th December 1859. He was the 5th son of Hugh Fortescue, the 3rd Earl Fortescue, and his wife Georgiana. He spent his childhood at Castle Hill near Filleigh in Devon. His family owned large areas of Exmoor. He attended Harrow School 1873-1878 and then went on to study law at Cambridge University in 1878. In 1880 he was appointed as private secretary to Sir William Robinson, who was Governor of the Windward Islands. John Fortescue spent 2 years in the Caribbean and then returned to Cambridge to complete his degree and graduated in 1884.
From 1886-1890 he lived in New Zealand, working as private secretary to Sir William Jervois, who was the Governor of New Zealand. During this time John Fortescue wrote several articles for Macmillan's Magazine, many of which were on the subject of military history, a subject which greatly interested him. He was then commissioned by Macmillan to write a comprehensive history of the British army. This was published in 13 volumes between 1899 and 1930. He also wrote several other books, including The Story of a Red Deer (a children's book published in 1897), My Native Devon (published 1924) and a biography of the Duke of Wellington (published in 1925).
In 1905 he was appointed as librarian at Windsor Castle by King Edward VII. He remained in this job until 1926. He accompanied King George V and Queen Mary on their 1911 visit to India and he wrote the official account of their visit.
In 1914 John Fortescue married Winifred Beech but they had no children. He often stayed at Simonsbath Lodge (this is now the Simonsbath House Hotel). He was knighted in 1926. He died in Cannes on 22nd October 1933 and his ashes were scattered at Five Barrows above Simonsbath. His widow suggested that his family should pay for a memorial cairn. This was built at the side of the Simonsbath to South Molton road above Drybridge Combe. The cairn and the land around it now belong to Exmoor National Park and they restored the cairn in 2001.