Ennis made the announcement Thursday in an email from the university.
"I'd like to thank coach (Jim) Boeheim, the coaching staff, my teammates and the amazing fans of Syracuse for the opportunity to play at a great university like Syracuse," Ennis said in the statement released by the school. "I feel this experience has helped prepare me to fulfill my lifelong dream -- to play in the NBA."
Ennis finished second on the Orange in scoring at 12.9 points per game and averaged 5.5 assists to go with 1.7 turnovers, one of the top assist-to-turnover marks in the nation.
"He sat down with us and we talked about it," Ennis's father, Tony McIntyre, said Thursday. "He feels like he's in a good place in the draft. There are not too many point guards and he feels that he can be valuable to a team in this year's draft."
McIntyre said the family spoke with Boeheim before announcing the decision.
"He just said he'd be there to help Tyler in anything he needs," McIntyre said.
A native of Brampton, Ontario, the 6-foot-2, 180-pound Ennis displayed an uncanny calmness for a freshman in leading the Orange to a school-record 25 wins to start the season and a No. 1 ranking for three weeks.
Ennis's 3-pointer at the buzzer beat Pittsburgh in mid-February. He took the team's last shot of the season, missing a 3 from the top of the key at the final horn in a 55-53 loss to Dayton in the third round of the NCAA tournament last Saturday night in Buffalo, N.Y. Syracuse finished 28-6.
"He did a great job here," Boeheim told The Post-Standard of Syracuse. "We're very proud of him. We'll move on."
One of those who wasn't surprised was Mark Taylor, Ennis's coach at St. Benedict's Prep in New Jersey.
"He's going to be a lottery pick. My gut would have been two (years at Syracuse)," Taylor told The Associated Press at midseason. "The numbers he's putting up, it's going to be hard for him not to go. He's going to be forecast to go so high in the draft, he might have to go just because it's so much money."
Ennis joins Carmelo Anthony and Donte Greene as the only Syracuse players to enter the NBA after their freshman season.
Still, it won't be so easy to leave.
"It's hard because he loves Syracuse," McIntyre said. "He loves playing there, he loves the fans, he loves his teammates, and he loves coach — all the coaches. That's the hard part, but, you know, when you're a little kid and you play basketball, you want to play in the NBA.
"I think that part makes it somewhat easier because the reality of it is he's got the shot to do that this year."