Educated at a private school at Tarvin, near Chester, he learned drawing under Robert Crozier, of the Manchester Fine Art Academy.
He studied in Academie Royale, Antwerp under Theodore van Lerius (1855-6), and in 1860 he was joined by du Maurier at the Kunstakademie Düsseldorf, where Eduard Bendemann was professor.
[1] In 1881 Armstrong was appointed director for art at the South Kensington Museum in succession to Edward Poynter, and had an immediate impact on its teaching, with his concept that craft and design required separate instruction.
He supported the efforts of Walter Copland Perry to supply art students with models of antique sculpture, and implemented plans for a museum of casts.
He supported an initiative on enamelling, under Pierre Adrien Dalpeyrat in 1886, and with Sir John Donnelly the School of Art Wood-carving.