Niemi moved to North America in 2000 to continue his professional career. Niemi played two years in the Mighty Ducks organization, mostly with their minor league Cincinnati Mighty Ducks team, but was called up to Anaheim for a total of 29 games.
Niemi returned to Finland and returned to Jokerit for the 2002–03 season. After one season, Niemi transferred to Frölunda HC of Sweden, where he played five seasons including the 2005 Elitserien championship. The 2008–09 season was split between HC Lada Togliatti of the Kontinental Hockey League and Leksands IF of the Swedish league.
In 2009 Niemi returned again to Finland and Jokerit. He played five more seasons with Jokeriti to finish his career, retiring in 2014. In total, Niemi won two SM-liiga gold medals with Jokerit.
Niemi was member of the Finnish national team at several World Championships, as well as the 2006 Winter Olympics. He was a member of the 2006 silver medal team.