The club has inked the University of Massachusetts standout to a three-year, entry-level contract. He'll join the Avalanche immediately for their playoff series against the Calgary Flames.
Makar captured the Hobey Baker Award as the top NCAA Division I men's hockey player and helped the Minutemen reach the Frozen Four championship game, which they lost to Minnesota Duluth on Saturday night.
He racked up 49 points in 41 games during his sophomore season.
The Avalanche selected the 20-year-old defenseman fourth overall in the 2017 draft.