Eric David Harris was born in Wichita, Kansas. The Harris family relocated often, as Eric's father, Wayne Harris, was a U.S. Air Force transport pilot. His mother, Katherine Ann Poole, was a homemaker. The family moved from Plattsburgh, New York, to Littleton, Colorado, in July 1993, when Wayne Harris retired from military service.

The Harris family lived in rented accommodations for the first three years that they lived in the Littleton area. During this time, Eric met Dylan Klebold. In 1996, the Harris family purchased a house south of Columbine High School. Eric's older brother, Kevin, attended college at the University of Colorado at Boulder.