Belgian cyclist Frans Mintjens began his career with a third place finish at the 1966 edition of the Tour of Flanders for amateurs. Mintjens then won stages at the Tour de l’Avenir, in addition to riding in the Peace Race in 1967 and 1968. That same year he was part of the Belgian delegation for the Mexico City Olympics, where he placed 18th in the team time trial with his compatriots. In 1969 he turned professional, making his Grand Tour début at the 1969 Tour de France. Over the next six years he rode in five further editions of the Tour, in addition to five starts at the Giro d’Italia, and one at the Vuelta a España. His best performances came at the Giro, finishing 20th in both 1971 and 1972. Mintjens also rode in multiple classic races, finishing fifth at the Tour of Flanders in 1971.