Kopecky was born in Rumst in Belgium and grew up in both Schelle and Niel. She has Czech roots, as her great-grandfather moved to Flanders. Before she started cycling, Kopecky tried many other sports, including gymnastics, basketball, horseback riding, tennis and soccer.
From a young age, Kopecky focused on track cycling. At seventeen, she competed in her first international championship. At the European Junior Championships, she finished eighth in the omnium and sixteenth in the points race. At the same championship a year later, she won a bronze medal in the team pursuit alongside Kaat Van Der Meulen, Jesse Vandenbulcke and Saartje Vandenbroucke. At the same event, she also claimed gold in the individual pursuit and the points race.
At the same time, Kopecky was making a name for herself on the road. In 2012, she won the national junior time trial title and finished second in the road race. However, on the road, she wasn’t as successful as on the track during her junior years.
Starting at seventeen, Kopecky competed in elite track races. In 2016, she achieved her first major success by becoming the European champion in the madison with Jolien D'Hoore. She also won a bronze medal in the omnium at this championship. Earlier in the year, she won the omnium and points race at the European U23 Championships. Kopecky didn’t compete on the track at the 2016 Olympics, as the Belgian team didn’t qualify, and she was a reserve in the omnium. She did compete on the road, participating in both the time trial, where she finished 21st, and the road race, where she placed 45th.
In 2017, Kopecky became a World Champion on the track for the first time, winning the madison with Jolien D'Hoore. This was also the year she won her first World Cup races. However, until 2020, she was less successful on the track, failing to win medals at the European or World Championships and only winning one World Cup race in three years. During this period, she became increasingly successful on the road. In 2019, she won the Tour of Valencia and became the Belgian time trial champion for the first time. In 2020, she won both the Belgian time trial and road race championships.
Starting in 2021, Kopecky’s career really took off. At the World Championships on the track, she won the points race and also took second place in both the omnium and the elimination race. On the road, she also won many races this year, becoming the Belgian road and time trial champion again and winning the points classification in the Vuelta, among other achievements.
In 2022, she maintained her good form, becoming the European and World Champion in the elimination race. She also won the points race at the European Championships. At the World Championships, she was successful again, winning the madison with Shari Bossuyt. On the road, Kopecky won the Tour of Flanders and the Belgian time trial championship.
2023 was a very successful year for Kopecky. She once again became European and World Champion in the elimination race and also won the points race at the World Championships. Her road season turned into a dream year, winning races such as the Tour of Flanders, the first stage of the Tour de France Femmes, Omloop Het Nieuwsblad and the World Road Cycling Championship. In the Tour de France Femmes, she also finished second overall, behind her teammate Demi Vollering.