The title is the second consecutive for the Cardinals, who defeated three-time winner Middlebury at Stafford last season.
Plattsburgh (25-3-1) joins Middlebury (3) and Elmira (2) as the only teams to win multiple Division-III Women's Ice Hockey Championships.
The Cardinals got on the scoreboard first midway through first period as Laurie Bowler slapped her own rebound in mid-air past Valiant net minder Karine Turmel. Claire O'Connor and senior first-team All-American Julie Devereux assisted on the power-play goal.
Manhattanville (24-7-0) struck back quickly as Amanda Nonis scored her third goal of the weekend and 19th of the season 11 minutes into the first. Sarah Fullerton and Erin Brawley tallied assists on Nonis' man-advantage score.
Danielle Blanchard, also a first-team All-American and Laura Hurd, the Division III Player of the Year, put Plattsburgh up 2-1 as she scored her 28th goal of the season, on a one-timer from Stephanie Moberg. Sophomore Amber Ellis scored the eventual game-winner just 49 seconds later. Freshmen Kate Fairfield and Brittany Meade assisted on the goal.
Manhattanville's Natalie Zitek scored her 12th goal of the season 11:36 into the second period. The power play score was assisted by first-team All-American Danielle Nagymarosi and Monique Rafferty. The Valiants nearly tied the game late in the third period but a goal was disallowed as an official's whistle had already blown the play dead for a delayed penalty on Plattsburgh. The Cardinals were then faced with a 5-3 disadvantage for 1:38, which they were able to kill off.
Plattsburgh out shot the Valiants, 20-9, in the first period. Turmel made 17 saves, setting a Division-III Women's Championship Game record for saves in a period. Turmel finished the contest with 33 saves, and Cardinal goalie Danielle Beattie stopped 22 shots en route to her 21st victory of the year.