The proffesional career of Vansummeren, nicknamed Summie and The tall from Lommel, started at the 1st of September 2002 when he started as an intern at Domo-Farm Frites, there he was in the same team of Johan Museeuw.
After his intern period Vansummeren went on to ride for Quick-Step-Davitamon-Latexco in 2003. For this team he won Luik-Bastenaken-Luik U23, the youth version of the known cycling classic. In that year he also won the general classification in the Tour of Luik. At the U23 world championships in Hamilton, Canada he became 2nd behind Sergei Lagoetin. After riding another year for Relax-Bodysol, Vansummeren left and joined Davitamon-Lotto. For this team he rode his first Tour de France in 2005, he would finish 136th in the general classification. He did ride some good positions in the Tour Down Under and the Tour de Andalusia that year. The Year after he rode the Tour de France again, finishing in the 112th position overall. His best performances were the 32nd position in the stage to Montélimar and the 37th position in the last time-trail.
In 2007 he was victorious once again, this time in a team effort. Together with teammates Cadel Evans, Nick Gates, Christophe Brandt, Josep Jufré, Dario Cioni, Wim Van Huffel, he won stage 1b of the international road cycling week, a team time-trial over 11km. Vansummeren celebrated his first official single professional victory in the 2007 Tour of Poland, where he won the last stage toward Karpacz and thanks to this victory he overtook the other general classification contenders and achieved the overall victory.
Since then Johan Vansummeren would be a domestique at Silence-Lotto. He achieved great positions in Paris-Roubaix: in 2008 he finished as 8th and a year later he would finish 5th.
In august 2009 Johan Vansummeren signed a contract at Garmin to start riding as a GC contender in 2010. On the 10th of april 2011 Vansummeren won Paris-Roubaix, the biggest victory of his career.
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