Cameron Pettit stood alongside his lawyer and spoke only to answer a judge’s questions as he entered the plea.
Prosecutors allege that Pettit, 28, of West Hollywood, sold Miller cocaine and pills that contained the powerful opioid fentanyl two days before the 26-year-old rapper died of an accidental overdose in September 2018.
Pettit has been in custody since his September 4 arrest.
He is among three men charged in connection with Miller’s death and each faces a mandatory minimum sentence of 20 years in federal prison and the potential for life without parole if convicted.
Pettit was arrested on September 4 and charged with selling drugs, charges later updated with the more serious count of causing Miller’s death.
His lawyer John D Robertson declined to comment outside court.
Citing Instagram messages sent shortly after Miller’s death in which Pettit talks with a friend about disappearing or leaving the country, a judge has kept him in custody since his initial arrest, calling him a flight risk.
Two other men, Stephen Walter, 46, of Los Angeles, and Ryan Reavis, 36, of Lake Havasu City, Arizona, have also been arrested in the case and indicted on similar charges.
They have not entered pleas, and it was not clear when they would be arraigned.
The indictment alleged that Walter supplied the fentanyl and cocaine that Pettit sold to Miller and that Reavis, who lived in the Los Angeles area until earlier this year, acted as a middleman for the fentanyl sale.
Pettit on September 5 2018 sold Miller cocaine, Xanax and 10 blue pills that appeared to be oxycodone but contained fentanyl after the two had exchanged text messages a day earlier, according to his indictment.
Miller’s assistant found him unresponsive in his Los Angeles home on September 7 2018 and he was declared dead soon after.
Miller’s rhymes made him a beloved and respected figure among fans, including some of the biggest names in hip-hop.
The Pittsburgh native, whose real name was Malcolm James Myers McCormick, was in a two-year relationship with Ariana Grande, who after his death paid loving tribute to him on social media and in a song.