[4] His dissertation advisor was future Nobel laureate Emilio Segrè, and Robert Oppenheimer taught York's quantum mechanics class.

After a brief stint as an assistant professor of physics at his doctoral alma mater in 1951, he was selected by Ernest Lawrence to serve as the inaugural director of the University of California Radiation Laboratory, Livermore Branch (1952–1958).

An advisor to the Arms Control and Disarmament Agency in the 1960s, he returned to government service in earnest as the U.S. delegate to the Comprehensive Test Ban negotiations in Geneva, Switzerland (1979–1981); as part of this role, he was the chief U.S. negotiator in the unsuccessful effort to impose a comprehensive U.S.-Soviet nuclear test ban.

[7] York was director emeritus of the Institute on Global Conflict and Cooperation at UC San Diego and served as chairman of the university's Scientific and Academic Advisory Committee, which oversees activities at both Livermore and Los Alamos National Laboratories.

He also served on the board of the Council for a Livable World, a nonpartisan arms control organization in Washington, D.C. York occasionally guest lectured for UC San Diego and other institutions.