The musician, whose real name was Malcolm James McCormick, is believed to have died from an overdose, according to TMZ.
Miller recently released his fifth album, Swimming, and had a tour booked for October. He became famous for songs such as 'Frick Park Market' and 'Knock Knock,' and recently ended a two-year relationship with singer Ariana Grande.
His family have released a statement, saying, "Malcolm McCormick known and adored by fans as Mac Miller, has tragically passed away at the age of 26. He was a bright light in this world for his family, friends and fans. thank you for your prayers."
Below, celebrities, musicians and fans pay tribute to the star.