Bell, 32, was found dead on Aug. 29 in Tucson, Arizona, nine days after he was reported missing.
The singer-songwriter had been reported missing on Aug. 20 and was found
"in a shaded area of a parking structure" not far from where he disappeared, according to the medical examiner's report.
Pima County's Chief Medical Examiner determined Bell died three days before his body was discovered. The report, issued on Monday, noted that drug paraphernalia was found at the scene.
"In consideration of the known circumstances surrounding this death, the available medical history, and the examination of the remains, the cause of death is ascribed to fentanyl intoxication. The manner of death is accident," the medical examiner wrote.
Bell's death was first reported by his close friend and fellow musician Matt Kinman, who shared the news with the blog Saving Country Music.
Bell was born in Lexington, Ky., and spent most of his childhood in Wyoming. He debuted into the country music scene with his album "Don't Mind If I Do" in 2014, and soon after landed a record deal with Thirty Tigers in 2016.
Following his record deal, he released a self-titled album that gained him critical acclaim. However, his rise to stardom came to a pause once mental health issues arose.
In a statement after his death, Bell's family said "Luke suffered from the disease of mental illness, which progressed after his father's death in 2015."
"Luke was supported through his disease by a community of loving family and friends. Despite this, he was unable to receive the help he needed to ease his pain," the family statement said.
"Many had big plans for Luke, but Luke’s plans remained decidedly less aspirational. A tour was planned for the fall of 2016 to help promote the record, but it never went off," the blog shared.