Born in Cincinnati, Ohio, Riley graduated from the University of Cincinnati in 1932 before earning his M.L.A. from Harvard University. He began his career as a landscape foreman with the Civilian Conservation Corps before starting an independent practice in 1937. In 1947, Riley joined the Olmsted Brothers firm, where he worked on both private and public projects, taking a special interest in the design of campuses including the University of Mississippi, Sewanee: The University of the South, Millsaps College, and the corporate campuses of National Life Insurance Company and Berkshire Life Insurance Company. Riley became a partner of the firm in 1950 alongside Edward Clark Whiting, Carl Parker, Artemas Richardson, and Joseph Hudak. The partners assumed overall management of the Fairsted estate, the Olmsteds' home and office, and worked to revitalize much of the grounds following a series of hurricanes in the mid-twentieth century. Riley’s work on the Fairsted estate included drafting a set of plans that envisioned the possibility of separating the home from the offices, allowing the partners to sell the home. This plan was ultimately rejected by the Brookline Building Commission and the firm retained the entire estate. Riley retired from the Olmsted Brothers in 1961, after which time it was renamed Olmsted Associates, Inc. Outside of his work with the firm he served as a founding director of the Hubbard Educational Trust (now Hubbard Educational Foundation), an organization dedicated to fostering education in landscape architecture. Riley died of cancer at the age of 57.