Nationally Kupczyk won the Polish titles in the 800 m in 1971 and 1973, and in the 1500 m in 1970. His best personal best time was 1:46.3 minutes, achieved in July 1972 at Bislett stadion. At the 1972 European Indoor Championships he won a bronze medal in 4×720 m relay, together with Zenon Szordykowski, Krzysztof Linkowski and Stanisław Waśkiewicz. He competed at the 1972 Olympic Games, finishing seventh in the 800 metres event.