Harris will earn an average annual salary of $1.4 million.
The 22-year-old scored one goal and added 10 assists in 47 games with the Canadiens so far this season.
The Haverhill, MA native has 12 points (2 goals, 10 assists) in 57 career NHL games.
Drafted 71st overall by the Canadiens in 2018, the 5'11'', 189-pound blueliner made his NHL debut on April 2, 2022 in Tampa Bay.