Instead of completing his senior year at Eureka High School, Janssen moved to Windsor, Ontario to begin his first season with the Spitfires.

During the 2003–04 OHL season, Janssen joined the Guelph Storm, where he participated in the Memorial Cup tournament.

"[6] On March 30, 2007, Janssen injured his shoulder in a fight with Riley Cote of the Philadelphia Flyers and missed 4 games.

[7] On February 26, 2008, Janssen was traded by the Devils to his hometown team, the St. Louis Blues, for defenseman Bryce Salvador.

[10] Janssen signed as a free agent on a one-year contract with the Nottingham Panthers of the EIHL on August 15, 2015.