Stephen J. Mackwell (born June 5, 1956) is a researcher in geophysics, specializing in laboratory-based studies of the physical, chemical and mechanical properties of geological materials. He is also interested in the transport of fluid components in mantle and crustal rocks on the microscopic and macroscopic scales, and on the effects of such components on mechanical properties. He has authored or co-authored over 80 articles in international scientific journals and is an editor of a book on comparative climatology of terrestrial planets published by the University of Arizona Press.