The move wasn't much of a surprise after his stellar performance at the Final Four in San Antonio.
"I've decided to sign with an agent and enter the 2018 NBA draft," Wagner wrote for The Players' Tribune.
He also wrote in his native German, "Alle träume klingen verrückt. Bis sie wahr warden." It's a saying he took from a Dirk Nowitzki poster, and in English it means, "All dreams are crazy. Until they come true."
Wagner, a skilled 6-foot-11, 245-pounder from Berlin, contemplated leaving school after his sophomore season, when he averaged 12.1 points and 4.2 rebounds per game, but NBA executives told Wagner he was a likely second-round pick who might even go undrafted.
Wagner returned to Michigan and became a more well-rounded player this season, averaging 14.6 points and 7.1 rebounds while improving his toughness and defense.
At the Final Four, he improved his stock with a 24-point, 15-rebound performance in a win over Loyola-Chicago in the national semifinals. He finished with 16 points and seven rebounds in the loss to Villanova in the national title game.
Several NBA executives told ESPN that Wagner may have played his way into the latter portion of the first round. He is ranked as the No. 48 prospect in the ESPN Top 100.
"This wasn't an easy decision for me," Wagner wrote in The Players' Tribune. "I know people always say that, and maybe it sounds like they don't 100% mean it. But I'm telling you guys -- the idea of leaving Michigan, of leaving this community, is really tough. This place has really started to feel like home."