Harry was born 5 February 1887 in New Glasgow to J. Howard Cavanagh and Margaret Jean MacKay. He was a civil engineer educated at Dalhousie University and the Massachusetts Institute of Technology. He had engineering experience with the Virginia Bridge and Iron Company, the Nova Scotia Steel and Coal Company, and was assistant to H.H. Lane, Consulting Engineer, in the erection of the Eastern Car Company's plant at Trenton, Nova Scotia. He enlisted in the Canadian Engineers and was lieutenant in the first Canadian contingent. He was shelled and had to have his leg amputated due to gangarene poisoning. He died of his injuries in Kensal Green, London, 1916 and was buried there.