Born in Edinburgh in 1947, Onwin studied Drawing and Painting at Edinburgh College of Art (1966-1970). Following a period teaching in secondary education he returned to ECA and is now a professor.


Onwin became fascinated by salt marshes, not as the subject of conventional landscape painting, but rather as a phenomenon to study with a quasi-scientific approach. He is interested in the structures behind appearances: microscopic images, crystalline forms, and the slow changes of materials over time.