Hummel took a feed from Lewis Jackson and fired a 15-footer to break a 56-56 tie. A potential game-winning 3-pointer by Wildcats forward John Shurna bounced off the glass at the buzzer.
Terone Johnson scored 14 points, D.J. Byrd had 12 and Hummel added 11 as the Boilermakers (15-7, 5-4 Big Ten) snapped a two-game losing streak.
Drew Crawford scored a game-high 23 points for the Wildcats (12-8, 2-6), while Shurna added 15.
The loss was the third straight for Northwestern.