Media reports say the 26-year-old, who was open about his substance abuse, died from an apparent overdose.
The rapper, whose real name was Malcolm James McCormick, rose to fame after topping US charts with his debut album in 2011.
He released his latest record, Swimming, earlier this year and was due to go on tour.
"The music artist known as Mac Miller died today in his Studio City home," the LA County Department of Medical Examiner-Coroner said in a statement.
"In the late morning of September 7, Malcolm McCormick was found unresponsive.... authorities were called and Miller was pronounced dead at the scene at 11:51 (18:51 GMT).
"At this time, an autopsy is pending and a cause of death has not been determined."
Miller went through a well-publicised break-up with singer and girlfriend Ariana Grande earlier this year.
The pair, who met in 2012, collaborated on a number of songs and performed together at the One Love Manchester concert in 2017.
Charges were filed against the rapper last month after he was arrested in May for driving under the influence and hit and run.
Grande spoke out publicly about ending their "toxic relationship" after fans blamed her for his arrest.
"I am not a babysitter or a mother and no woman should feel that they need to be," she said in a typed message posted on social media.
Grande said she had "tried to support his sobriety" for years, and was praying that he "figures it all out".
An early beginning Born in Pittsburgh, Pennsylvania, Miller began to focus on his music while still at school and released his first mixtape under the name EZ Mac at just 15.
Maturing in the public eye, he starred in a MTV reality series in 2013 which followed him and a group of friends after he moved to Los Angeles to pursue his career.
He released a series of albums and EPs across the last decade, collaborating with high-profile artists like Kendrick Lamar and Pharrell Williams.
In his final tweets posted on Thursday, the rapper promoted the North American tour he was set to embark on next month.
He was "a bright light in this world for his family, friends and fans." his family said, in a statement confirming his death.
Artists including Snoop Dog, Wiz Khalifa and Shawn Mendes paid tribute to Miller after news of his death broke on Friday.
In a moving tweet, Chance the Rapper said he was "completely broken" after hearing the news and described Miller as "one of the sweetest guys I ever knew".
A lot of rappers don't make beats. A lot of beat-makers can't rap. Mac Miller could do it all, lending an uncommon intimacy to his best songs.
He started piano lessons at the age of six, later picking up drums, bass and keyboards. By the age of 15, he'd released his first mixtape, But My Mackin' Ain't Easy, but it was his fourth release, 2010's KIDS - a playful, freewheeling collection of party tunes that won him a recording contract.
Over the years, he shed his frivolous, frat-boy reputation, making increasingly mature, introspective records that dealt with his personal demons; as well as 2016's The Divine Feminine, a naive but affecting (and occasionally too-graphic) concept album about what he called "the feminine energy of the planet," but which many took to be a tribute to his partner, Ariana Grande.
In music, and in his interviews, he was open about his addictions - which eventually prompted Grande to end their relationship, describing it as a "toxic relationship". But Miller refused to exploit their break-up on his latest album, Swimming. "Everybody wants a headline / I don't got nothin' to say," he rapped on Programs, released in May, just weeks after their split was confirmed.
Instead, the album documented his ongoing struggles with substance abuse. "Got my head underwater, but I ain't in the shower, and I ain't getting baptised," he confessed on Jet Fuel. The halting vocals and fractured, subdued production made it clear he was suffering but there was always a sense of optimism - a promise that those demons could be beaten.
Tragically, it appears he lost the battle.