John Armstrong was born in Ireland in 1818 or 1819 and emigrated to Saint John, New Brunswick, in 1836. He became a merchant and the owner of John Armstrong and Company, a dry goods store located on Prince William Street, Saint John, from ca. 1849 until 1877 when it was engulfed during the Great Fire of Saint John in June that year.
He was married to Jane Jones, born in 1825 or 1826, and they had at least one child, Margaret born in 1848 or 1849. Armstrong owned land in Saint John, Woodstock, Grand Falls, Buctouche and areas of Carleton, Victoria, Kent, Queens and Sunbury counties. He had interests in sawmills and had owned or had shares in ships and boats, including the barque "Jennie Armstrong" and the brig "Maggie".
St. John Business Directory, 1857; Conwell, Russell H., History of the great fire in Saint John, June 20 and 21, 1877; and Census 1851