Mountaineers center Aaric Murray came in off the bench in the second half and finished with 10 points and five rebounds.
Henderson had all his points in the first half to help West Virginia (1-1) take a 51-19 halftime lead. The Mountaineers made 22 of 39 shots during the opening half, while Marist went 5 for 20.
Marist (1-3) got 10 points from Isaiah Morton. Adam Kemp had six points and nine rebounds.
West Virginia's margin of victory was the largest at the Old Spice Classic. The previous mark was set in 2010 when Texas A&M beat Iona 74-55.
Juwan Staten converted a pair of free throws midway through the second as West Virginia went up 65-26. Harris' layup made it 81-36 with four minutes to play.
Henderson had a slam dunk and then hit a 3-pointer as West Virginia took a 24-9 advantage eight minutes before intermission. Harris had a 3-point play, slam and layup to extend the Mountaineers lead to 37-14.
Kevin Noreen scored after a rebound, Matt Humphrey had a fastbreak slam and Henderson added two baskets during a 12-0 run that put West Virginia ahead 15-6 with 13 minutes left in the first half.
Humphrey finished with 10 points and teammate Jabarie Hinds had 11.