The 20-year-old hip-hop star, whose real name is Jahseh Onfroy, was reportedly gunned down while shopping for motorcycles in Deerfield Beach, Florida.
In a statement released on Twitter, the Broward Sheriff's Office said: "The adult male that was taken to the hospital has been pronounced dead.
"The adult male victim has been confirmed as 20 year old Jahseh Onfroy aka rapper #XXXTentacion."
Earlier, police had said they had been called to the scene of a shooting at 3671 North Dixie Highway in Deerfield Beach.
They received a call at 3.57pm local time and Onfroy, born in Plantation, Florida, was taken to hospital but later pronounced dead.
Onfroy's short career was overshadowed by alleged incidents of domestic violence and at the time of his death he was facing 15 felony charges.
They included counts of false imprisonment, aggravated battery of a pregnant woman and domestic battery by strangulation, for alleged incidents involving his ex-girlfriend in 2016.
Onfroy released two studio albums, 17 and ?, with the latter reaching number one on the Billboard 200 chart in March.
In May, he was one of the artists temporarily removed from Spotify's playlists due to its policy of not promoting artists with a history of alleged hateful conduct, before Spotify withdrew the policy.