Poirier, a native of Salaberry-de-Valleyfield, Quebec, was selected by the Flames in the third round, 72nd overall, in the 2020 NHL Draft. The 19-year-old is currently a member of the Saint John Sea Dogs (QMJHL), where he finished last season second on his team in scoring with nine goals and 28 assists for 37 points over 33 games. Poirier's draft year saw him notched 20 goals and 33 assists for 53 points in 64 games in 2019-20, finishing the season with the most goals by a defenceman in the QMJHL.