Percy was the second son of the 6th Duke of Northumberland and his wife Louisa Drummond, daughter of Henry Drummond of Albury Park, Surrey. He was educated at Eton and Christ Church, Oxford. From 1872 to 1880, he was a lieutenant in the Grenadier Guards. He was Major in the part-time 3rd (Royal Berkshire Militia) Battalion, Royal Berkshire Regiment from 1881 to 1886. He was also J.P. for Surrey.Debretts Guide to the House of Commons 1886Emma Elizabeth Thoyts, History of the Royal Berkshire Militia (Now 3rd Battalion Royal Berks Regiment), Sulhamstead, Berks, 1897/Scholar Select, ISBN 978-1-37645405-5, pp. 207–8, 213, 304.
