Armia would spend three years in Finland, playing with Porin Ässät. During that time, he would have career totals of 55 goals, 45 assists, for 100 points, with 120 penalty minutes. In 2012–13, Armia would score 19 goals and 14 assists in 47 games. He was instrumental in helping Ässät capture the SM-Liiga’s Kanada-malja championship after finishing fourth in the regular season. In the playoffs, Armia scored three goals with five assists in 16 playoff games.
NHL
On 16 June 2012, Armia was signed to a three-year entry level contract with the Buffalo Sabres. During his second North American professional season in 2014–15, Armia was recalled from Buffalo's American Hockey League affiliate, the Rochester Americans, and made his NHL debut with the Sabres against the Detroit Red Wings on 23 December 2014. He was then returned to the Americans before being traded on February 11, 2015, the Sabres sent Armia, alongside Tyler Myers, Drew Stafford, Brendan Lemieux and a conditional first-round draft pick in 2015, to the Winnipeg Jets in exchange for Evander Kane, Zach Bogosian and the rights to goaltender Jason Kasdorf. On 30 June 2018, the Jets traded Armia, alongside Steve Mason, a seventh-round draft pick in 2019, and a fourth-round pick in 2020 to the Montreal Canadiens in exchange for Simon Bourque. On 13 July 2018, Armia signed a one-year contract worth $1.85-million with the Canadiens. On 6 October 2018, Armia scored his first goal for Montreal, a shorthanded goal that gave the Canadiens a 4-0 lead over the Pittsburgh Penguinsen route to a 5-1 victory. On 1 November 2018, Armia and Habs teammate Max Domi scored the fastest two goals by one team when Montreal defeated the Washington Capitals, 6-4. Domi scored at 19:38 of the third period, and Armia clinched the win with an empty net goal two seconds later. Armia converted the decisive goal in the fifth round of a shootout victory against the New York Islanders on 5 November 2018; he was the only player from either team to beat the goaltender. However, in the Canadiens' next game, against the New York Rangers on 6 November 2018, Armia suffered a knee injury. He was initially expected to miss six to eight weeks, and ultimately missed twenty-five games. On 3 January 2019, Armia returned from injury against the Vancouver Canucks; he was credited with an assist on Jordie Benn's opening goal in a 2-0 Montreal win. On 1 March 2019 Armia scored his first career NHL hat trick in a 4–2 victory against the New York Rangers. On 11 July 2019, Armia signed a two-year contract worth $5.2 million with the Canadiens. He had previously filed for salary arbitration as a restricted free agent. Armia scored his first two goals of the 2019-20 season in a 4-5 overtime loss to the Buffalo Sabres on 9 October 2019.
