He spent several years there, making his professional debut in 2018 with the GCK Lions of the Swiss League, the second tier of hockey in Switzerland.

In 2018 he moved to North America and spent two seasons with the Ottawa 67's of the junior Ontario Hockey League (OHL).

At the age of 10 Rossi moved to Switzerland to further his career, and Feldkirch, his hometown, is close to the Austria–Switzerland border.

At the age of 13 Rossi moved to Zürich again to help his career, with him and his father commuting two hours each way in order to allow Marco to stay at home and continue his education.

[5] Rossi returned to Ottawa for the 2019–20 season and led the OHL, and the entire CHL in scoring with 120 points in 56 games.

[6] He was the first European player to lead the OHL in scoring (Stan Mikita, who was born in Slovakia and raised in Canada, did so in the 1958–59 season).

[17] He returned to the under-18 level for the 2018 Division IB tournament, recording 7 points in 5 games to place second for Austria and tied for fourth overall.

[18] Rossi served as Austria's captain during the 2021 World Junior Ice Hockey Championships.