Internationally, he played for the Finland men's national ice hockey team, and was inducted into the IIHF Hall of Fame in 2024.

After successful World Championship tournament in 1995 Nummelin attracted some international publicity and was contracted by Frölunda HC, a Swedish team playing in the Elitserien.

Nummelin played in Lugano for 5 seasons (2001–06) and won several honors during that time, such as the overall scoring title in 2004 and the Swiss championship in 2003 and 2006.

Although Nummelin displayed both strong offensive and defensive contributions during regulation play, many consider his strongest asset his ability to score in the overtime shootout.

As of 7 December 2006, Nummelin converted six shootout goals in all six of his attempts, beating some of the NHL's best goalies including Nikolai Khabibulin, Roberto Luongo and Vezina winner Miikka Kiprusoff.

Nummelin's opportunity in the shootout initially came as a shock to fans and teammates when Minnesota Wild head coach Jacques Lemaire listed him third in the shootout lineup against the Vancouver Canucks on 10 October 2006, in the place normally given to Marian Gaborik (the first three shooters are often reserved for the team's best goal scorers).