Kapanen was selected by the Pittsburgh Penguins in the first round (No. 22) in the 2014 NHL Draft after he had 14 points (seven goals, seven assists) in 47 games with KalPa of Liiga, Finland's top pro league.

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Penguins general manager Jim Rutherford also drafted Kapanen's father, Sami Kapanen, in the fourth round (No. 87) in the 1995 NHL Draft as the Hartford Whalers GM. Sami, who had 458 points (189 goals, 269 assists) in 831 games during 12 NHL seasons and played in the Stanley Cup Final with the Carolina Hurricanes in 2002, played alongside his son at KalPa in 2013-14.

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On July 11, 2014, Kapanen signed a three-year, entry-level contract with the Penguins.

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Kapanen played for KalPa in the 2014-15 season and had 21 points (11 goals, 10 assists) in 41 games before appearing in four games with Wilkes-Barre of the American Hockey League.

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On July 1, 2015, Kapanen was acquired by the Toronto Maple Leafs in a trade that sent forward Phil Kessel to the Penguins.

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Kapanen played for Finland in the 2016 IIHF World Junior Championship and had five points (two goals, three assists) in seven games. He scored the game-winning goal 1:33 into overtime against Russia to give Finland the gold medal.

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He played in 44 games and had 25 points (nine goals, 16 assists) for Toronto of the AHL in 2015-16 and was called up by the Maple Leafs on Feb. 29, 2016. Kapanen made his NHL debut that night against the Tampa Bay Lightning.

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The following season, Kapanen had 43 points (18 goals, 25 assists) in 43 games for Toronto of the AHL and appeared in eight games for the Maple Leafs, scoring his first NHL goal in a 5-3 win against the Penguins on April 8, 2017. In Game 2 of the Eastern Conference First Round against the Washington Capitals, Kapanen scored the game-winning goal at 11:53 of the second overtime. He had two goals before the Maple Leafs were eliminated from the Stanley Cup Playoffs in six games.

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Kapanen played 38 games in 2017-18 and had nine points (seven goals, two assists), as well as one goal in seven Stanley Cup Playoff games. After the season, he played for Finland at the 2018 IIHF World Championship and scored three goals in eight games.

When forward William Nylander remained unsigned for the first two months of the 2018-19 season, Kapanen used the opportunity to claim a regular spot with the Maple Leafs, scoring 20 goals and finishing with 44 points in 78 games. He followed that with 13 goals and 36 points in 69 games in 2019-20.

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NOTES & TRANSACTIONS

 

• Traded to Toronto by Pittsburgh with Nick Spaling, Scott Harrington, Pittsburgh's 1st round pick (later traded to Anahem -- Anaheim selected Sam Steel) in 2016 NHL Draft and New Jersey's 3rd round pick (previously acquired, Toronto selected James Greenway) in 2016 NHL Draft for Phil Kessel, Tyler Biggs, Tim Erixon and Pittsburgh's 2nd round pick (previously acquired, Pittsburgh selected Kasper Bjorkqvist) in 2016 NHL Draft, July 1, 2015.

• Traded to Pittsburgh by Toronto with Pontus Aberg and Jesper Lindgren for Evan Rodrigues, Filip Hallander, David Warsofsky and Pittsburgh's 1st-round pick in 2020 NHL Draft, August 25, 2020.