The Demons (13-13 overall, 9-6 in the Southland) trailed 19-10 early, but rallied to lead 38-35 at halftime and never trailed again.
White led five players in double figures: Zeek Woodley with 12, with 11 each by Jalan West and DeQuan Hicks, and 10 by Gary Stewart.
Northwestern hit 64 percent after halftime to offset 65 percent aim by the Lions (11-15, 6-9), who drained 11 of 23 from 3-point range and 16 of 20 free throws.
Southeastern's Dre Evans scored a game-high 26, 18 on 6 of 11 aim behind the arc, while Julian Chiera hit 4 of 5 from distance in a 16-point night.
All of West's scoring came after halftime, including four in the final minute, a step-back 12-footer with 50 seconds to go and two free throws with 31 seconds left to rebuild six-point advantages each time.
NSU didn't turn the ball over in the final four minutes as SLU had chewed a 17-point deficit down as close as three points.
It got that close twice, but each time the Demons answered immediately and the Lions never had the ball with a chance to tie.
"It was a really good place for us to be, in a close game late, and we didn't falter," said Demons coach Mike McConathy. "We made adjustments, we were able to get things done out of timeouts, and we won a tough road game against an extremely well-coached team."
The Demons owned a 37-24 rebounding advantage as Woodley had five and six Demons snatched four, including backup post player Ryan King and West, who had five assists and two steals.
"Early we didn't compete well, but Ryan King came off the bench and ignited us with his effort, and it caught fire," said McConathy. "Collectively we stepped up and did a lot of good things, and then showed some backbone down the stretch when the home team made a really good rally."
The Demons roared to a 68-51 advantage with 10:36 remaining with a 17-3 run, but the Lions answered with a 15-2 burst and the margin ranged between six and three points in the final 6:44.
White sank 9 of 15 shots, despite going 1 of 5 on 3-pointers, while posting his sixth career 20-point game.
SLU became only the third team in 10 games to top 74 points and the third to shoot better than 40 percent against Northwestern.
The Demons play their final regular-season road game, and end a string of five in a row, Saturday at 6:15 at New Orleans.
The last two regular-season contests are at home in Prather Coliseum next Thursday against Central Arkansas and next Saturday afternoon against Oral Roberts, with NSU trying to complete season sweeps against those teams.