Marcel Grifnée began his cycling career with several podiums in amateur races in the late 1960s, including becoming the Belgian team time trial champion in 1968. For his performance in the latter Grifnée was selected to ride in the same event at the Mexico City Olympics, where Belgium placed 18th. The following year he rode in the Peace Race, finishing in the top 10 on two stages. He remained an amateur throughout his brief career, finishing on the podium at multiple races in Belgium before retiring from the sport.