Classen played four seasons of junior hockey for the Nipawin Hawks of the SJHL. He then went on to play two seasons of hockey at Merrimack Collegecompeting in the Hockey East Division of the NCAA. While at Merrimack, he earned a spot on the Hockey East All Rookie Team. After going undrafted, Classen signed as a free agentin 1999 with the NHL‘s Nashville Predators. He spent his first five pro seasons in the Nashville Predators organization, splitting time between the parent club and the Milwaukee Admirals. In 2004 Classen signed with Finland's SM-liiga club Ässät. Returning to the Admirals for 2005–6, he played the following season in Germany with DEL club, the Hamburg Freezers. On July 3, 2007, it was announced he had signed a contract with the Vancouver Canucks. He was then reassigned by the Canucks, and played with their American Hockey League affiliate, the Manitoba Moose. He moved to fellow AHL team Providence Bruins the following season and after 1 game moved onto the San Antonio Rampage before leaving for German team, Iserlohn Roosters, where he spent the remainder of the 2008-09 campaign. He started the 2009-10 season with the Rapperswil-Jona Lakers of the Swiss top flight, before transferring to second-division side EHC Basel Sharks during the season. In January 2010, he moved on to another Swiss team, HC Sierre-Anniviers. On July 18, 2010, Classen returned to the German DEL and signed a two-year contract with Kölner Haie. After three seasons with Haie, Classen left as a free agent to sign with ERC Ingolstadt. In 2014, he joined German second-division side Lausitzer Füchse on a two-year deal. On March 14, 2015, he was attacked with a knife and severely injured. He was hospitalized for almost a month and returned to game action in September 2015. Classen left the Füchse squad upon the conclusion of the 2015-16 campaign and was signed by fellow DEL2 side Starbulls Rosenheim on August 27, 2016. Classen moved on to a Player-Assistant Coach role for two seasons with the Rostocker EC Piranhas of the German Eishockey-Oberliga.
