 Born on 13 March 1887, he was the eldest son of Charles William Mills, 2nd Baron Hillingdon (1855–1919) who served as Conservative Member of Parliament for Sevenoaks from 1885 to 1892, and his wife Alice Marion Harbord, daughter of Charles Harbord, 5th Baron Suffield.He processed at the coronation of Edward VII and Alexandra in 1902 with Lord Suffield who was Master of the Robes.He joined the family bank Glyn, Mills, Currie & Co. in 1910.