Tyrone Lewis added 13 points and Demetrius Williamson had 12 for the Purple Eagles (25-7, 15-4 MAAC).
The game was never in doubt for Niagara, which led wire-to-wire and went into the second half on a 10-0 run that bridged the halftime break. Benson Egemonye added 11 points and nine rebounds.
Ryan Schneider scored 12 points - including his 1,000th career point, which came on a late 3-pointer - and grabbed 12 rebounds for the Red Foxes (10-23, 5-15 MAAC). They also got 12 points from Kaylen Gregory and 10 from David Devezin.
Marist shot just 33 percent from the floor and 36 percent (9-for-25) from the free-throw line.
Niagara took a 39-23 lead into the break.