Born in Chicago, Illinois, Riley earned a B.Phil. from the University of Chicago in 1949 before studying architecture at the Massachusetts Institute of Technology. After earning a B.Arch. in 1954, he served as a captain in the U.S. Air Force before joining the architecture firm Kea, Shaw, Grimm & Crichton in Hyattsville, Maryland. In 1964 Riley relocated to Albuquerque, New Mexico, where he ran his own architectural firm, American International Assurance. Shortly afterwards he joined the faculty of the University of New Mexico, first as a campus planner and then as an associate professor of architecture, eventually serving as the founder and director of the university’s Center of Environmental Research and Development. In 1970 Riley joined the University of Illinois at Urbana-Champaign as a professor of landscape architecture and architecture, a position he held until his retirement in 1996. He also headed the Department of Landscape Architecture and directed the doctoral program. As head of the department, he led the State of Illinois’ first comprehensive inventory of natural land and water areas in 1976. Additionally, he taught as a visiting professor at both the University of Melbourne, in Australia, and the Harvard University Graduate School of Design. Outside academia, Riley served as president of the Council of Educators in Landscape Architecture from 1984 to 1985 and as the chair of the Environmental Design Research Association in 1991. He was also a member of the Senior Fellows Committee. From 1966 to 1970 he was the associate editor of the publication Landscape, and he was the editor of Landscape Journal from 1987 to 1989. In 2015 Riley published Camaro in the Pasture: Speculations on the Cultural Landscape of America. He was named a Fellow of the American Society of Landscape Architects in 1993. Riley died at his home in Urbana, Illinois, at the age of 88.