In 1968 Leijn Loevesijn entered the Olympics as the Dutch champion in the kilometre time trial and the tandem sprint, earning a silver medal in the tandem at Mexico City. In 1969 he placed second in the Dutch championships in both the tandem and kilometre and then turned professional. As a pro he became best known as a six-day racer, although he continued to compete in track sprints, winning the Dutch professional sprint title consecutively from 1970-76. He was world sprint champion in 1971 and won a bronze medal in that event in 1970. Loevesijn had multiple top finishes in six-days but struggled to get onto the podium. He retired after 1976 but came in 1979, with his final major event the 1979 World Sprint Championships, in which he finished sixth.