Hays was born in Johnstown, New York, and educated at Harvard, Ohio State, and Columbia universities, obtaining his PhD from the last in 1964. He joined Columbia's Lamont–Doherty Geological Observatory, New York, in 1967 as director of the deep-sea sediments core laboratory and in 1975 was appointed professor of geology.

In 1971 Hays reported that from his study of 28 deep-sea piston cores from high and low latitudes it was shown that during the last 2.5 million years eight species of radiolaria had become extinct. Prior to extinction these species were widely distributed and their sudden extinction, in six out of eight cases, was in close proximity to a magnetic reversal, a change in the Earth's magnetic polarity. Hays concluded that the magnetic reversals influenced the radiolarians' extinction.