 Cordeaux was born into a gentry family descended from Edward I, the second son of Colonel Edward Kyme Cordeaux (1866-1948), CBE, DL, JP, of Brackenborough Lawn, Louth, Lincolnshire, High Sheriff of Lincolnshire in 1925, late of the Lincolnshire Regiment, and Hilda Eliza Agar, MBE, daughter of Sir Henry Bennett, of Grimsby and of Thorpe Hall, Louth.His paternal grandfather was the ornithologist John Cordeaux.Cordeaux served in World War II in the Royal Marines, reaching the rank of Lieutenant Colonel.