As an amateur, Gerard Koel’s greatest success came at the 1964 Olympics, where he competed in the team pursuit on the track, earning a bronze medal. He turned professional in 1966, primarily racing in six-days events. During his career, which would last until 1974, he won two six-days. In 1967 he won in Madrid (with Jan Janssen), and in 1973 in Amsterdam (with René Pijnen and Leo Duyndam). He also earned Dutch titles on the track, winning the spring in 1968 and 1969, and the scratch in 1970. After his active career, he acted as a chauffeur for Dutch television during the Tour de France.