In 1951 Belgian cyclist Robert Grondelaers won the overall classification at the Tour de Namur ahead of compatriot Lucien Victor. Both Grondelaers and Victor, along with André Noyelle and Rik Van Looy, were selected to represent Belgium in the road race at the 1952 Helsinki Olympics. At the Games Noyelle won the road race, 47 seconds ahead of Grondelaers, with Victor just missing out on a medal in fourth, with Belgium also winning gold in the combined team event.
In 1953 Grondelaers finished second on stage six of the Tour of Belgium before winning stage 12 of the Tour of Britain. One year later he turned professional, signing a contract with the Belgian team Plume Sport. His professional career lasted until 1962, although Grondelaers did not have any wins during this time.