Peter Libby was born in Berkeley, California, on February 13, 1947, and grew up in that city as well. He graduated in 1969 from the University of California (UC), Berkeley with a bachelor's degree in biochemistry and French literature, and earned his medical degree in 1973 from UC, San Diego. He trained in internal medicine and in cardiovascular diseases at the Peter Bent Brigham Hospital (now Brigham and Women's Hospital [BWH]) in Boston. During medical school, he was active in research, and continued this during his residency and fellowship.