The deal carries an AAV of $842,500 with a $92,500 yearly signing bonus factored in.
Leason was the Capitals’ second-round pick (No. 56 overall) at June’s NHL draft.
The 20-year-old recorded 89 points in 55 games with the Prince Albert Raiders in the WHL last season.
The six-foot-four, 210-pound forward added 25 points in 22 post-season games, good for second in the league, as the Raiders captured the Ed Chynoweth Cup as the WHL champions.
The Calgary native also starred for Team Canada at the 2019 world juniors, potting five points in five games.