She gained her first experience in competitions, international level, at the U18 World Championships 2015 in Cali , where she reached the semi-finals over 400 meters. A year later she also reached the semifinals over 400 meters at the U20 World Championships in Bydgoszcz and took sixth place with the Polish 4 x 400 meter relay. In 2017 Natalia Kaczmarek took part in the U20 European Championships in Grosseto , where she finished seventh over 400 meters and fourth in the Polish relay. In 2018 she was part of the Polish relay at the World Indoor Championships in Birmingham , where she won the silver medal. It was also used in the run-up to the European Championships in Berlin in August and thus contributed to winning the gold medal. The following year she improved at the U23 European Championships in Gävle to 52.34 s and won the gold medal in the individual competition and also won the relay in 3: 32.56 min.