Born in Webb City, Missouri in 1911, Riley was educated within the state at Drury College and Washington University in Saint Louis, graduating with a Mississippi in embryology. Working with the ecologist G. Evelyn Hutchinson, he completed his doctoral thesis on the copper cycle of lakes in Connecticut.
He moved to Yale University in 1934, intending to work with the anatomist Ross Harrison, but instead became interested in limnology. He continued to be interested in the productivity of lakes, but gradually increased his studies to encompass salt water, ultimately becoming a biological oceanographer. Riley"s oceanographic work focused on the influences affecting the population ecology of plankton systems in coastal and open ocean waters.
His early work correlated phytoplankton production with regulating factors such as nutrients, light and zooplankton abundance.
From this empirical base he went on to develop ecosystem models that explained the annual cycle of plankton ecosystems, most notably in his analysis of the Georges Bank region. After an extended period at Yale, in 1965 Riley moved to become a professor, and the director, at the Institute of Oceanography at Dalhousie University.
Much of his work continued to be in collaboration with researchers at the Woods Hole Oceanographic Institute. Towards the end of his life, Riley wrote a candid autobiography of his scientific life, in part to document the early days of oceanography.
