Cornell was born in Palo Alto, California and is a distinguished alumnus of both Cambridge Rindge and Latin School (1976-1979) and San Francisco's Lowell High School (1979-1980). He received his B.S. in Physics with honour and distinction from Stanford University in 1985 and Ph.D. in Physics at MIT in 1990. He is currently a professor at the University of Colorado and a physicist at the United States Department of Commerce National Institute of Standards and Technology. His lab is located at JILA. He was awarded the Lorentz Medal in 1998 and is a Fellow of the American Association for the Advancement of Science.
In October 2004, his left arm and shoulder were amputated in an attempt to stop the spread of necrotizing fasciitis, sometimes referred to as "flesh-eating disease." He was discharged from the hospital in mid-December, having recovered from the infection, and returned to work part-time in April 2005.