Kupczak completed his first international race on February 27, 2010 at a Continental Cup competition in Karpacz , where he finished 39th. He made his debut in the Nordic Combined World Cup on November 30, 2013 in Kuusamo, Finland . Kupczak took part in the 2013 Winter Universiade in Trentino . There he finished 23rd in the Gundersen competition on the normal hill and fifth in the mass start. Together with Paweł Słowiok and Adam Cieślar , he won the team competition. At the Universiade 2015 he reached third place in the individual and fourth in the team with Cieślar and Mateusz Wantulok. A month later he achieved 37th place in the Gundersen competition on the normal hill at the Nordic World Ski Championships 2015 in Falun .
The 2018/19 World Cup season was very successful for Kupczak. So he regularly demonstrated his jumping skills, so that he was ultimately the sixth best ski jumper among the combiners. However, his poor mileage often threw him back, which is why he only reached 35th place in the overall standings. At the Nordic World Ski Championships 2019 in Seefeld , he took 25th place on the large hill on the Gundersen and 18th place on the normal hill. In addition, he was eighth in both the team sprint and with the team.
In summer 2019 , Kupczak reached the podium at the highest level for the first time when he finished third behind Franz-Josef Rehrl and Akito Watabe at the mass start in Klingenthal . He achieved this placement again a few days later at the Gundersen competition in Oberhof . He finished the overall Grand Prix ranking in a strong ninth place. In winter , too, Kupczak was the only competitive Polish combined athlete in the World Cup circuit, but he also occasionally reached the points, but initially could not confirm his performances from the summer. Only after a strong jump in the Nordic Combined Triples at the end of January 2020 in Seefeld did he achieve his best individual result in twelfth place.