In impressing through the Under-20 Junior A level, Koppanen was selected by the Boston Bruins in the fifth round, 135th overall, in the 2016 NHL Entry Draft.

[1] He was initially returned on loan by the Bruins to his original club, Ilves, to make his professional debut in the 2017–18 Liiga season.

On 14 March 2018, he was reassigned to make his North American debut in joining the Bruins AHL affiliate in Providence.

[3] Showing his offensive acumen, Koppanen registered 6 goals and 17 points in 10 games before he was elevated on loan to affiliate and former club, Ilves of the Liiga, on 28 October 2020.

[7] Leaving the Bruins organization at the conclusion of the season, Koppanen was signed as a free agent to a two-year, two-way contract with the Pittsburgh Penguins on 1 July 2023.