Born the oldest of four children in Detroit, Michigan, Cowan's family moved to St. Louis, Missouri, where he began his education attending public schools.

[3] Cowan was a captain in the United States Army Air Forces, where he earned a bronze star in World War II.

In the following year, he joined the staff of the British Branch of the MIT Radiation Laboratory, which was located in Great Malvern, England.

The pair, and their collaborators, collected data for months, and in 1956, concluded that they had certainly observed the neutrino, publishing their work in the July 20, 1956 issue of Science.

The following year he left GWU and joined the faculty of The Catholic University of America in Washington, D.C., a post he held until the end of his life.

His grandson, James R. Riordon [d], a science journalist[8] and a former physicist and engineer who heads the American Physical Society media relations office, initially conceived of the distributed computing project Einstein@home, which searches gravitational wave data for signals from massive rotating objects such as pulsars.