Coach Willie Taggart made the announcement on Sunday in a statement posted on the school's website.
Blackman beat Wisconsin graduate transfer Alex Hornibrook and Louisville transfer Jordan Travis. The redshirt sophomore will start for the Seminoles when they open the season against Boise State on Saturday in Jacksonville.
It isn't clear if Hornibrook or Travis will be FSU's backup. Taggart's next opportunity to meet with the media is on Monday.
Blackman has started 13 games, including 12 as a true freshman in 2017. He has thrown for 2,740 yards, 24 touchdowns and 12 interceptions at FSU.
In his only 2018 start, Blackman threw for 421 yards, four touchdowns and an interception in a road loss to NC State. Blackman became the immediate odds-on favorite this winter, when Taggart dismissed Deondre Francois, who started 11 games last fall, after a social media post included audio of an alleged argument between the quarterback and his girlfriend.
After Francois was injured in the 2017 opener, Blackman started as a true freshman and improved down the stretch as he led the Seminoles to a win at Florida and a bowl victory over Southern Miss.
But Francois won the job back last fall, and Taggart opted to stick with Francois for the remainder of the 2018 season. The Seminoles missed out on a bowl game for the first time since 1981.
Blackman thinks he has a strong grasp of what new offensive coordinator Kendal Briles wants to run. Even though Blackman has had three offensive coordinators and varied schemes in his short career, he told reporters during preseason camp that he has an understanding of "what to do and when to do it and how to do it" when it comes to Briles' high-tempo spread offense.
And he's learning the scheme without a playbook. In fact, everyone is.
It's a new wrinkle for Florida State in 2019, something Taggart has embraced -- and so have the players.
"It's a great thing not having a playbook because you have to go and make sure you write up the plays by yourself," Blackman said. "And go study by yourself and make your own playbook. Guys are really putting in the work to learn and understand your job."
The Associated Press contributed to this report.