Eric David Harris was born on April 9, 1981, in Wichita, Kansas. His parents, Wayne and Katherine, were originally from Colorado. Wayne Harris was a transport pilot in the United States Air Force. In 1983, the family moved to Dayton, Ohio, when Eric was just two years old. They continued moving, relocating to Oscoda, Michigan, in 1989. While in Oscoda, they had a good rapport with their neighbors. A local pastor, William Stone, described the Harris family as "great neighbors" who were well engaged in their community.

In 1991, they moved to Plattsburgh, New York. As Eric attended Stafford Middle School, he played Little League Baseball and participated in various social activities, feeling like a typical kid. In 1992, the family settled back in Littleton, Colorado, where Wayne Harris retired. In an English class assignment in 1997, Eric expressed his feelings about moving from New York to Colorado, calling it difficult and leaving him feeling alone and lost.

Eric had a chest deformity known as pectus excavatum, which caused him to be self-conscious, especially in gym class where he avoided taking off his shirt due to ridicule from classmates. To address the issue, he underwent two cosmetic surgeries at the ages of 12 and 13. When the family first arrived in Littleton, they lived in rented housing for three years. During seventh grade, Eric met Dylan Klebold, and they quickly became friends.

In 1996, the Harris family bought a house near Columbine High School. Eric's older brother, Kevin, was a college student at the University of Colorado at that time. Eric began attending Columbine High School as a freshman in 1995. The school had recently undergone renovations. Eric soon made a name for himself on the soccer team and had a number of friends. One of his early crushes was on a girl named Tiffany Typher, who he asked to homecoming. After the dance, she lost interest in him, which upset Eric.

On April 20, 1999, Eric Harris and Dylan Klebold carried out a tragic event at Columbine High School in Colorado. Their plan began earlier in the year, with a focus on creating a significant impact. They had created explosive devices, including two large propane bombs, which they left in the school cafeteria.

On the day of the attack, Harris and Klebold arrived at the school shortly before lunch. They left the duffel bags with the bombs in the cafeteria and took positions outside. Their original plan involved the bombs detonating first, which would create chaos, allowing them to target students and staff as they fled the building. However, the bombs failed to explode.

With their initial strategy compromised, Harris and Klebold began shooting students and staff indiscriminately. The school went into lockdown as gunfire erupted, causing panic throughout the building. Many students were injured, and thirteen people lost their lives that day—twelve students and one teacher.

After the shooting, the two gunmen moved around the school, targeting those they encountered. They eventually entered the library, where more students were held captive. Shortly afterward, they took their own lives as law enforcement responded to the situation outside.

This event was the deadliest school shooting in U.S. history at the time and left a lasting impact on the nation. Harris was confirmed to have killed eight of the victims, while Klebold was responsible for five. Additionally, there were many injuries, 24 in total, including some who were critically hurt. The aftermath of this tragedy impacted many families and changed policies regarding school safety across the country.