Career
Dumoulin has been a professional since 2002, for the Jean Delatour team At the end of 2003 he moved to AG2R Prévoyance before riding for Cofidis. Dumoulin left Cofidis at the end of the 2012 season, after five seasons with the team, and signed a two-year contract with Ag2r–Louisiana Mondiale for the 2013 and 2014 seasons.
Dumoulin rode as an amateur for the TCCT (Tonic cyclo club of Ternay).
He dropped out of the 2004 Tour de France when he crashed after hitting a dog. Recovery took him four months and he did not race for the rest of the season.