It was first produced in 1940 by Glenn T. Seaborg, Edwin M. McMillan, Joseph W. Kennedy, and Arthur C. Wahl at the University of California, Berkeley.

They bombarded uranium with deuterons (heavy hydrogen nuclei) in a cyclotron to produce neptunium-238, which then decayed into plutonium-238.

Plutonium is not found in nature, although trace amounts of plutonium-244 have been detected in uranium ores.