Dr Mark Chavez has pleaded guilty to conspiring to distribute ketamine that led to Matthew Perry's fatal overdose.
Chavez entered the plea on Wednesday, and faces up to 10 years in prison. He will be sentenced in April 2025.
The former doctor - he has agreed to surrender his medical licence - is one of five individuals to be charged in the aftermath of Perry's October 2023 death and the third to admit guilt.
Last month, Perry's assistant Kenneth Iwamasa and Perry's acquaintance Erik Fleming both pleaded guilty to conspiracy to distribute ketamine resulting in death. Dr Salvador Plasencia and the so-called Ketamine Queen, Jasveen Sangha, pleaded not guilty.
Chavez, Iwamasa and Fleming have agreed to cooperate with the investigation in exchange for lesser charges as federal prosecutors go after Plasencia and Sangha, whom they deem to be primarily responsible for Perry's death.
Chavez's lawyer said during an earlier court appearance that Chavez is "incredibly remorseful" and "trying to do everything in his power to right the wrong that happened here".
According to court documents obtained by Us Weekly, Plasencia allegedly contacted Chavez about buying ketamine in September 2023 after learning that Perry "was interested in obtaining" the drug.
"I wonder how much this moron will pay," Plasencia allegedly texted Chavez.