[2] He worked as a chemist for the Clinton Laboratories (now Oak Ridge National Laboratory) during the World War II Manhattan Project, engaged in separating, identifying and characterizing the radioactive elements produced by nuclear fission.

[2] In 1945, he, together with Jacob A. Marinsky and Charles D. Coryell, isolated the previously undocumented rare-earth element 61 (promethium).

[1][3][4] Marinsky and Glendenin produced it both by extraction from fission products and by bombarding neodymium with neutrons.

In September 1947, Marinsky and Glendenin announced the discovery at a meeting of the American Chemical Society.

He served as Scientific Secretary for the U.S. delegation to the Atoms for Peace Conference[2] and received the American Chemical Society's Glenn T. Seaborg Award for Nuclear Chemistry in 1974.