JoAnne L. Hewett (born 1960) is a theoretical particle physicist on the faculty of the SLAC National Accelerator Laboratory at Stanford University, where she is a professor in the Department of Particle Physics and Astrophysics. Since 2017 she has been the associate lab director of the Fundamental Physics Directorate and the chief research officer at SLAC. Her research interests include physics beyond the Standard Model, dark matter, and hidden dimensions. She is a fellow of the American Physical Society and a fellow of the American Association for the Advancement of Science (AAAS).

In April 2023, she was named as the next director of Brookhaven National Laboratory and president Brookhaven Science Associates, taking over these roles from Doon Gibbs.