Niewiadoma started racing bikes with local club WLKS Krakus BBC Czaja and soon emerged as one of the most promising women riders in Poland. In 2013, she won two national Under-23 champion titles, finishing 4th in both the elite time-trial and elite road race. She also finished 5th in European Road Championships in the women's Under-23 road race. Following these performances, she received an offer from professional team and became a stagiaire in August 2013. She participated in the Boels Ladies Tour, finishing 10th overall and winning the young rider classification. Niewiadoma was also selected for the UCI Road World Championships but she did not finish the elite women's race.
Niewiadoma signed a one-year contract with in October 2013 and made her debut in professional ranks in February 2014. She took her first victory four months later, winning the Swiss race GP Gippingen. Preparing for Giro d'Italia Femminile, Niewiadoma participated in the Polish National Championships, taking bronze in the elite women's time trial and finishing 8th in the road race. Her climbing abilities proved to be an asset for the team, as she worked for the final victory of Marianne Vos on the mountain stages in Italian Alps. She finished 11th overall and 3rd in the young riders classification, marking a successful debut in the biggest race of the elite women's calendar in her first year as a professional. Niewiadoma then went on to take her first podium spot in a stage race. Together with Anna van der Breggen and Vos she dominated racing during the 1st edition of Ladies Tour of Norway and placed 3rd, winning the best young rider classification and the best climber standings. In September, she signed a two-year contract extension with the team and concluded preparations for the World Championships with a start in the Premondiale Giro della Toscana, placing 8th overall. On a hilly route in Ponferrada she led the Polish team in the women's elite road race, coming to the finish in 11th place after a sprint from the selected group.
2015
In her second year as a professional Niewiadoma shone as one of the best young riders in the peloton, giving Poland results it had never had in women's cycling. She once again demonstrated her climbing abilities with 6th place in the inaugural edition of Strade Bianche Donne and 5th in the prestigious World Cup race La Flèche Wallonne Féminine. She also took a podium spot in the Dutch race Boels Rental Hills Classic, finishing behind Lizzie Armitstead and Emma Johansson. In June she won Emakumeen Euskal Bira, a five-day stage race in the Basque Country, and won silver in the elite women's road race at the European Games. Despite being only 21, Niewiadoma started the season's biggest race – the Giro Rosa – as one of 's leaders. She quickly assumed the lead of the young rider classification and held on to the top places on the mountain stages. She then clocked the fifth-fastest time on the demanding route of stage 8, a time trial, and climbed up to 4th overall with just one mountaintop finish to go. The long climb to San Domenico di Varzo proved decisive and Niewiadoma crossed the line in 7th, finishing 5th overall, winning the white jersey for best young rider and celebrating Anna van der Breggen's overall success. With those results under her belt Niewiadoma led the Polish national team at the European Road Championships in Tartu and took gold in the women's under-23 road race, bridging to the leading group on the last lap and claiming the sprint ahead of Italy's Ilaria Sanguineti and fellow rider Thalita de Jong. She concluded the season at the World Championships in Richmond, being a part of a squad that secured bronze in the team time trial event. She also led the Polish team in the elite women's road race and sprinted to 7th place.
