Joel Smithers, a 36-year-old father of five, was arrested at his southern Virginia practice in 2017.
In May, he was found guilty on more than 800 counts of illegally prescribing drugs, including the oxycodone and oxymorphone that killed a West Virginia woman.
Smithers’ mandatory minimum sentence is 20 years.
Officials said Smithers was part of an interstate drug distribution ring throughout West Virginia, Kentucky, Ohio, Tennessee and Virginia.
"I went and got medication without — I mean, without any kind of physical exam or bringing medical records, anything like that," a woman who said she became addicted after getting pills from Smithers testified in court.
His office was described in court as lacking medical supplies and having patients who slept outside and urinated in the parking lot.
"People only went there for one reason, and that was just to get pain medication that they (could) abuse themselves or sell it for profit," Christopher Dziedzic, a supervisory special agent for the Drug Enforcement Administration who oversaw the investigation into Smithers, said.
"He's done great damage and contributed ... to the overall problem in the heartland of the opioid crisis," he added.
Smithers didn’t accept insurance and made more than $700,000 from his patients in two years.
During his trial, he testified that when he moved to Virginia he was inundated with patients from other states that said their pain clinics had been shut down.
He testified that he reluctantly treated them and said if he wasn’t able to examine them he spoke to them over the phone.
He said that he had been deceived by some of his patients.
"I learned several lessons the hard way about trusting people that I should not have trusted," he testified.
Once, Smithers met a patient in a Starbucks parking lot and for $300 gave her a prescription for fentanyl, a pain reliever up to 100 times more potent than morphine, he said.
Smithers worked out of the small city of Martinsville, which had the nation’s third-highest number of opioid pills per capita between 2006 and 2012.
He previously had complaints at his former practice in West Virginia, but when authorities came to his office with a subpoena they found a dumpster filled with shredded documents and untested urine samples.
Smithers is scheduled to be sentenced Wednesday.
Opioids have killed about 400,000 people over the last 20 years.
The Associated Press contributed to this report.