Maassen began his racing career with success in Formula Ford, winning the Belgian championship in 2001 and 2002.

Having competed in selected Eurocup Formula Renault 2.0 in the previous two seasons, Maassen moved to the series full-time in 2005, finishing tenth overall.

Maassen stepped up to the Formula Renault 3.5 Series in 2007, but failed to score any points in 17 starts for Prema Powerteam.

Maassen also raced for Luc Alphand Aventures at the 2009 24 Hours of Le Mans, finishing second in the GT1 category.

[1] Maassen competed in the new FIA GT1 World Championship in 2010, returning to the DKR Engineering team, now under the Mad-Croc Racing banner.