The 19-year-old has now made his decision, although he will have the opportunity to withdraw from the draft by June 15.
An Italian native, Mannion first gained national attention in the United States as a high school player, becoming a viral sensation thanks to his athleticism:
He was rated the top point guard prospect and No. 9 overall player in the 2019 class, per 247Sports' composite rankings.
The high level of play continued at Arizona, where he averaged 14.0 points, 5.3 assists and 1.2 steals per game.
It was enough for Bleacher Report's Jonathan Wasserman to consider him the No. 20 overall prospect in the class heading into March.
At 6'3", 190 pounds, Mannion is slightly undersized for the NBA, and his outside shooting was a bit inconsistent at 32.7 percent this season. On the other hand, the guard showcased good athleticism with the ability to attack the basket and finish with ease.
Adding in his quality work on the defensive end, he has a chance to be an impact player in the pros.
His departure will also leave Arizona especially short-handed next year after it lost much of the rotation from the 2019-20 squad, including seniors (Dylan Smith, Stone Gettings, Chase Jeter, Max Hazzard) and other top draft prospects Zeke Nnaji and perhaps Josh Green, who has yet to decide. Miller will have a tough challenge getting the Wildcats back into contention in the Pac-12 with a lot of turnover during the offseason.