The Los Angeles County coroner's report named Miller's cause of death as "mixed toxicity" of the three substances found in his system.
The 26-year-old Pittsburgh native, who frankly discussed his depression and addiction in his rhymes, died suddenly on Sept. 7. He was known to many as Ariana Grande's ex-boyfriend, but had a devoted following that included some of the biggest names in hip-hop.
Miller's personal assistant, making a daily visit to Miller's home in the San Fernando Valley section of Los Angeles, found him unresponsive on his bed at about 11:30 a.m., the report states.
The assistant moved the body to the floor and performed CPR at the direction of a 911 operator. Paramedics soon arrived and Miller was declared dead 16 minutes after the initial 911 call.
The report says a police investigator found an empty bottle of liquor and drug paraphernalia, including a $20 bill with white powder residue on it that was in Miller's pocket.
The report notes that Miller's many tattoos included one of an hourglass on his arm with the words, "Only so much time left in this crazy world."
The rapper, whose real name was Malcolm James Myers McCormick, was generally healthy otherwise, the report stated. He had a history of drug and alcohol abuse, but his mother told investigators he had not overdosed in the past to her knowledge, or been hospitalized for any reason.
Miller's mother told a coroner's investigator that she had spoken to him the night before his death, and that he had been in good spirits, seeming very excited about a new album and upcoming tour.
Miller's assistant agreed, saying Miller was feeling positive about his projects, but said he had a tendency to slip into drug binges, and had such an episode three days before the one that left him dead.
The autopsy was performed three days after Miller's death, but the cause of death was deferred while toxicology tests were performed.
He is the latest musician whose death has been linked in recent years to a national wave of opioid abuse and overdoses. Prince died in 2016 when he took counterfeit pills laced with fentanyl that looked like a generic version of the painkiller Vicodin.
Miller's autopsy report did not address where he might have gotten the fentanyl or cocaine.
Matthew Roberts, guitarist for the band 3 Doors Down, also died of an overdose in 2016, and had fentanyl and hydrocodone in his system.
Miller's death brought mourning and tributes from musical luminaries. Performers at a concert in his honor last week included Chance the Rapper, Travis Scott and John Mayer. The concert launched the Mac Miller Circles Fund in honor of the hip-hop star and raised money for arts education in underserved communities.
He was in a two-year relationship with Ariana Grande that ended earlier this year. She posted an affectionate video of him on her Instagram page weeks after his death, and released a new song, "Thank U, Next ," on Saturday that mentioned Miller along with "Saturday Night Live" star Pete Davidson, her fiance until recently. In the song, she pays tribute to Miller.
"Wish I could say thank you to Malcolm," the song says. "Cause he was an angel."