Born at Carmarthen, South Wales, in 1860. He was educated at Hereford School and University College, London, and at University College Hospital, where he served as house surgeon. He practised for a time at Hereford and served as a ship's surgeon with the Peninsula and Oriental Company. He went to Australia in 1892 and practised at Hay and later at Tamworth, New South Wales, as an ophthalmic surgeon. About 1905 he settled at Hobart, Tasmania, where he practised for the rest of his life, specializing as an ophthalmologist, and was for many years district naval surgeon. Armstrong married Isobel, daughter of C M Maxwell, and was survived by two sons, both practising ophthalmologists, Dr Keith B Armstrong at Sydney, Australia, and Dr Hugh Maxwell Armstrong at Bedford, England. He died suddenly of a heart attack, while visiting a patient at Hobart, on 6 April 1935, aged 75. He was buried at Hobart after a funeral service in St David's cathedral.