The 6-foot-2 Canadian informed Orange coach Jim Boeheim of his decision Thursday afternoon.
"I'd like to thank Coach Boeheim, the coaching staff, my teammates and the amazing fans for the opportunity to play at a great university like Syracuse," Ennis said in a statement released by the school. "This experience has helped prepare me to fulfill my lifelong dream to play in the NBA."
Ennis wasn't on the radar for many NBA executives, but he had a terrific freshman season and was key in Syracuse's starting 25-0. The Orange struggled down the stretch and lost to Dayton in the third round of the NCAA tournament.
Ennis, a true point guard who averaged 12.9 points, 5.5 assists and 3.4 rebounds per game, is projected to be a lottery pick by ESPN NBA Insider Chad Ford.
"It'll probably come down to him and Marcus Smart as far as the top point guard taken in the draft," one NBA general manager told ESPN.