The Green Knights made their trip back to the championship game count in Patrick Gym on Sunday.
Rice used a second-half rally to jump ahead of St. Johnsbury and hang on in the final moments and beat the Hilltoppers 53-51.
RMHS had missed the previous three finals after making six straight appearances from 2011-16. Most recently, the Knights fell to St. Johnsbury in a 55-54 thriller in the 2019 semifinal game.
With the win, Rice took home its 16th D1 title in program history, and first since 2015.
Junior guard Michel Ndayishimiye posted a game-high 20 points in the win, including the deciding field goal with just over 30 seconds left in regulation.
This contest was also the first time a D1 championship game was decided by two points or fewer since 2004, when Mt. Mansfield edged Burlington 46-45.