Mason made a 3-pointer that gave Niagara a 60-56 lead and sparked a 14-5 run during which Mason hit two more to put the Purple Eagles up 70-61 with 2:59 left.
Niagara went ahead 47-40 with 14:31 left to play, but Marist took its first lead of the second half at 51-50 on Khallid Hart's layup with 9:47 to go.
The teams exchanged the lead three times and tied twice before Marcus Ware's free throw gave Niagara (6-15, 3-7 Metro Atlantic Athletic Conference) the lead for good at 57-56.
Chavaughn Lewis had 25 points to lead Marist (6-13, 3-6) which shot 28 of 52 from the floor and out-rebounded the Eagles 31-27, but couldn't overcome 16 turnovers.
Maryland point guard Melo Trimble has withdrawn from the NBA draft and will return to College Park for his junior season, sources told ESPN.
Louisville's Chinanu Onuaku, who recently underwent a medical procedure to correct a heart rhythm issue detected during the combine, will keep his name in the NBA draft pool.
Andrew White III will return to the Nebraska men's basketball team next season after removing his name from the NBA draft.