In the 1960s and 1970s Otakar Mareček represented Czechoslovakia at three Olympic Games in rowing. Mareček made his first Olympic appearance at the 1968 Mexico City Games as part of the crew in the eight that finished fifth. Four years later he was part of the coxed fours that won bronze at the 1972 München Games. At the 1976 Montréal Olympics the Czechoslovak team narrowly missed out on another medal in the coxed fours when they finished fourth. Mareček also enjoyed success at the European Championships, winning bronze in the eight (1963) and in the coxed fours (1965, 1973). After his rowing career he served as the chair of the national rowing union from 1988 to 1996, and was a member of the executive committee of the Czech Olympic Committee. In 2014 Mareček was bestowed with the title of Honorary Member of the Czech Rowing Association.