Blommaert started figure skating in 1998. He started out as a single runner for Belgium at the European Championships in 2008 and 2009 and also at the Junior World Championships in those years. In 2011 he switched to pair skating and found a partner in Annabelle Prölß . Since then he has started for Germany. The couple immediately won the German junior championships in pair skating in 2012 and the German championships in the master class a year later. The couple's coach was Karel Fajfr . They trained in Oberstdorf and started for the EC Oberstdorf. The couple split in 2014.
Mari Vartmann and Ruben Blommaert became German champions in 2017. Then the couple separated and, although qualified, no longer competed in the European championships. Since the beginning of 2017 he has been training with Annika Hocke alternately in Berlin with Knut Schubert and in Oberstdorf with Alexander König . The couple separated in 2019.