A native of Montreal, Poirier began his junior hockey career with the Gatineau Olympiques of the Quebec Major Junior Hockey League in 2011–12. He appeared in 67 games, scoring 15 goals and 40 points. Previously unheralded, Poirier improved to 70 points in 65 games in 2012–13; he was the team's scoring leader, 16 points ahead of his nearest teammate. He established himself as a top-40 prospect for the 2013 NHL Entry Draft. The NHL Central Scouting Bureau placed him 39th in their final pre-draft list, and Poirier moved higher in the projections with a standout performance in the playoffs; he had ten points in ten playoff games, including six "highlight reel" goals. Capable of playing at either the wing or at centre, Poirier is a fast skater, though he says his style is "not pretty". Describing his playing style, Poirier stated: "I love to play hard. I compete, got to the net hard and fight a little bit, too. I want to bring energy." He was invited to attend summer camp for the Canadian national junior team ahead of the 2014 World Junior Ice Hockey Championships. At the draft, Poirier was selected in the first round by the Calgary Flames, 22nd overall. Returning to Gatineau, Poirier had his best season as a junior in 2013–14. He set career highs and led his team with 43 goals, 44 assists and 87 points to go along with a plus-minus rating of +30. He also signed an entry-level contract with the Flames, and joined Calgary's American Hockey League affiliate, the Abbotsford Heat on an amateur try-out agreement after Gatineau was eliminated from the QMJHL playoffs. Poirier scored a goal in his first professional game, then added another to go with two assists in his second as the Heat prepared for the AHL playoffs. Following the season, the Flames announced that Poirier had played the year with a bad shoulder that required surgery. Poirier missed the first month of the 2014–15 season while recovering. He was assigned to the AHL's Adirondack Flames when healthy and scored twice in his first game. The 20-year-old forward scored 30 points in his first 42 games with Adirondack and was the youngest player in the AHL All-Star Game. He was recalled to Calgary on February 23, 2015, and made his NHL debut the following night in a 1–0 loss to the New York Rangers. Poirier recorded his first NHL point with an assist on a goal by Mikael Backlund on March 3, 2015, against the Philadelphia Flyers. After his fourth full season within the Flames organization, Poirier was released as a free agent when he was not tendered a qualifying offer as a restricted free agent. Un-signed over the summer, Poirier without an NHL deal, accepted a professional try-out contract to begin the 2018–19 season, with the Manitoba Moose, affiliate to the Winnipeg Jets, on October 4, 2018. Poirier was limited to just 24 games through injury, registering 8 points. As a free agent following a full season with the Moose, Poirier was unable to secure a contract over the summer. Returning to attend the Manitoba Moose training camp, Piorier was signed to a professional tryout contract to begin the 2019–20 season on October 4, 2019.
