John L. Hennessy is the President of Stanford University, where he has been a member of the faculty since 1977 in the Departments of Electrical Engineering and Computer Science. Hennessy is a fellow of the IEEE and ACM, a member of the National Academy of Engineering, and a fellow of the American Academy of Arts and Sciences. He received the 2001 Eckert-Mauchly Award for his contributions to RISC technology, shared the John von Neumann award in 2000 with David Patterson, and received the 2001 Seymour Cray Computer Engineering award.

Hennessy's original research group at Stanford developed several of the techniques now in commercial use for optimizing compilers. In 1981, he started the MIPS project at Stanford with a handful of graduate students. After completing the project in 1984, he took a one-year leave from the university to co-found MIPS Computer Systems, which developed one of the first commercial RISC microprocessors. After being acquired by Silicon Graphics in 1991, MIPS Technologies became an independent company in 1998, focusing on microprocessors for the embedded marketplace. As of 2001, over 200 million MIPS microprocessors have been shipped in devices ranging from video games and palmtop computers to laser printers and network switches.

Hennessy's more recent research at Stanford focuses on the area of designing and exploiting multiprocessors. He helped lead the design of the DASH multiprocessor architecture, the first distributed shared-memory multiprocessors supporting cache coherency, and the basis for several commercial multiprocessor designs, including the Silicon Graphics Origin multiprocessors.