Steve Janssen was a catcher in the Belgian leagues, beginning his career at their highest level (First Division) in 1987 at age 15. He played on 7 national champions in Belgium before retiring in 1997. He played in several European Cups with the Brasschaat Braves and European Championships with the Belgian National Team. He hit .367/.429/.633 in the 1993 European Championship with 3 triples, 8 runs and 7 RBI in 8 games. He led the tournament in triples (only two other players had more than one), tied Antonio Salazar and David Meurant for 5th in total bases (19) and was 4th in slugging (between Javier Diez and Paolo Ceccaroli). He was 0 for 1 in the 1995 European Championship). In both 1998 and 1999, he managed the Brasschaat Braves; they won the Belgian Championship in 1999. From 2000-2003, he coached the DOOR Tridents in the Netherlands' Eerste Klasse. In 2003, he became the pitching coach for the Dutch national team till 2005; in this period he was part of two gold medals during the 2003 European Championship and 2005 European Championship and competing in the 2004 Olympics in Athens.
In 2006, he was third base coach with DOOR Neptunus. He was technical director of the Belgian Baseball Federation in 2007. For 2008, he was hired as Manager of Sparta/Feyenoord and led them to a 21-21 record. DOOR Neptunus then brought him back, this time as their head coach, replacing Eric de Bruin. He was named Coach of the Year in 2009 after managing Neptunus to the 2009 Holland Series title. In 2010, Steve managed Neptunus to another title with a regular season 39-3 record and 4-2 in the 2010 Holland Series. Since 2010, Steve is back with the Dutch national team as their Pitching Coach; he helped them win the Gold medal during the 2011 Baseball World Cup in Panama and reached the semis during the 2013 World Baseball Classic where he handled the pitchers together with Hall of Famer Bert Blyleven and was the bullpen coach during the games. He managed the Netherlands in the 2014 European Championship. He is either a cousin or nephew of Marc Janssen (Dutch source describe the relationship as 'neef', which could be either cousin or nephew in English), who had preceded him as a catcher for Belgium's national team.