Harold Stanley Cayzer, the youngest son and last child of Sir Charles Cayzer, 1st Bt, was born on 8th August, 1882. He was educated at Cargilfield School in Edinburgh and subsequently became a professional soldier in the 11th Hussars. On 5th December, 1908 he married Mary Kate Dudgeon of Merville, Co. Dublin and had two children, Stanley and Mary.
As a consequence of his military career he was at first only nominally involved in the family firm of Cayzer, Irvine & Co. but on leaving the Army, in 1913, he was appointed a manager of the company. This role was cut short, however, by the outbreak of the First World War when he was recalled to his old army regiment seeing service in France, from where he wrote vivid letters back to his family leaving them in no doubt as to the terrible conditions of war. In 1915 he was promoted to the rank of Major. In that same year a shell exploding near him brought on severe concussion and he was invalided back to England. Once returned to health, he was sent as a staff officer to Egypt, attached to the Mediterranean forces.
In 1918 he returned to civilian life and began to play a leading part in the management of the family firm. He made his home at Dunchurch Lodge in Warwickshire and served as High Sheriff of the county in 1935. Continuing his love of horses and hunting, he became Master of the Pytchley Hunt. In 1943, following the death of his brother, August, Harold became vice-chairman of Cayzer, Irvine & Co. He died during a visit to South Africa in February 1948.