Harison was born at Sutton Place, Seaford, East Sussex. He first arrived in the Cape of Good Hope in 1849 as a captain in the Perthshire Regiment (later the 2nd Battalion of the Black Watch, Royal Highland Regiment) to take part in the Eighth Frontier War (1850–1853). He resigned his commission on returning to England, married Louise Marie Millett Moorman, the daughter of a naval officer, and returned to Cape Agulhas to breed horses. The stud farm was not a success, and Harison joined the Government Forest Service. In 1856 was appointed Conservator over a large section of the Southern Cape forests, namely the Tsitsikamma forests eastward to Alexandria. His headquarters were located at Witelsbos near Storms River. In 1874 he became Conservator of a newly created conservancy including the forests of George, Knysna and Humansdorp. In 1888, he transferred to Tokai in Cape Town as Conservator over the Western Conservancy.