Grimmie was signing autographs with band members of Before You Exit, with whom she performed earlier, when a gunman approached and opened fire before her brother tackled him at the Plaza Live music venue, the Orlando Police Department said on Twitter.
Grimmie died from her injuries, the department said in a post early Saturday.
The suspect shot and killed himself, police tweeted.
Grimmie placed third during the 2014 season of the "The Voice," a singing competition on NBC.
"We are heartbroken," said "The Voice" in a Twitter post late Friday.