A speedy forward with natural scoring ability and good size at 6-foot-4 and 213 pounds, Armia has increased his goal production each season of his NHL career.

The Canadiens acquired him in a trade with the Winnipeg Jets on July 1, 2018. He scored 13 goals and had 10 assists in his first season with Montreal, including his first NHL hat trick in a 4-2 win against the New York Rangers on March 1, 2019. He helped the Canadiens to the 2021 Stanley Cup Final, a five-game loss to the Tampa Bay Lightning, and signed a four-year, $13.6 million contract with Montreal on July 27, 2021. He scored his 100th NHL goal in a 3-1 win at the Dallas Stars on Jan. 16, 2025, and was named to Finland's roster for the 4 Nations Face-Off.

Armia signed a two-year, $5 million contract with the Los Angeles Kings on July 1, 2025, and helped Team Finland win bronze at the Olympic Winter Games Milano Cortina 2026 with a team-high eight points (three goals, five assists) in six games. He had a goal and two assists in a 6-1 win against Team Slovakia to become the seventh player with three points in a medal game during the Olympics with NHL players and first since Slovakia's Pavol Demitra in the bronze-medal game at the 2010 Vancouver Games.

In three seasons with the Jets, the Pori, Finland, native had 58 points (26 goals, 32 assists). He scored two goals in 13 Stanley Cup Playoff games for the Jets in 2018.

Armia was selected by the Buffalo Sabres in the first round (No. 16) in the 2011 NHL Draft.

After three productive seasons with Assat Pori of Liiga, Finland's top league, Armia transitioned to North America for the 2013-14 season. He made the Sabres out of training camp, but a hand injury sidelined him for 20 games. By the time Armia was healthy, Buffalo opted to send him to Rochester of the American Hockey League.

He made his NHL debut the next season in a one-game appearance for the Sabres against the Detroit Red Wings on Dec. 23, 2014. Armia delivered four hits in 14:47 of ice time in Buffalo's 6-3 road loss.

Less than two months later, the Sabres traded Armia to Winnipeg as part of the Feb. 11, 2015 deal that sent Evander Kane to the Sabres. Armia remained in the AHL until Winnipeg called him up for his Jets debut on Dec. 18, 2015.

Armia's first NHL goal was a game-winner on Jan. 2, 2016 in a 4-1 victory against the San Jose Sharks. He had his first two-goal game on Feb. 25, 2016, adding an assist as the Jets defeated the Dallas Stars 6-3.

Timely offense is something Armia grew used to delivering earlier in his career. In 2012-13, his 19 goals ranked second on Assat Pori. Armia had eight points in 16 postseason games to help Assat win its first league championship since 1978.

The second-youngest player on Finland's 2011 World Junior Championship team at 17, Armia represented his country at the tournament three times. At the 2013 World Junior Championship, he finished second with six goals and 12 points in six games.