Michael Stewart Witherell (born 22 September 1949) is an American particle physicist and laboratory director.

[1] In 1985 Witherell led an experiment at Fermilab which was the first to isolate a large sample of particles containing the charm quark using the new technology of silicon microstrip detectors.

[1] In January 2016, the University of California Board of Regents appointed him to be the Director of Lawrence Berkeley National Laboratory.

Witherell served on the National Academies' Committee on Science, Engineering, Medicine and Public Policy (COSEMPUP) from 2017-2021.

[6] His wife Elizabeth Witherell, a literary historian and scholarly editor, is editor-in-chief of The Writings of Henry D. Thoreau project at UC Santa Barbara.