Routt County Coroner Robert Ryg said that 37-year-old Austin Eubanks died overnight at his Steamboat Springs home.
There were no signs of foul play. An autopsy is planned to determine the cause of death.
Mr Eubanks was shot in the hand and knee in the Columbine attack that killed 12 classmates and a teacher, including his best friend.
He became addicted to drugs after taking prescription pain medication while recovering from his injuries.
He later worked at an addiction treatment centre and travelled across the US telling his story.
Mr Eubanks’ family says in a statement that he “lost the battle with the very disease he fought so hard to help others face”, KMGH-TV reported.
The family added: “We thank the recovery community for its support. As you can imagine, we are beyond shocked and saddened and request that our privacy is respected at this time.”