Mareczko was born in Poland on 30 April 1994; he moved with his mother to
Brescia, Italy, when he was five years old. Racing as an amateur cyclist in the 2013 and 2014 seasons, he won 16 races and came to the attention of
Davide Cassani. He was the most successful under-23 rider in Italy in 2014. Mareczko's first wins as a professional cyclist came in the 2015
Vuelta al Táchira (a
2.2 race where many of the riders are amateurs), where he won stages 3 and 4. Mareczko won two stages at the
Vuelta a Venezuela, a 2.2-ranked race. His first professional-level victory came at the end of the 2015 road racing season, when he won the sixth stage of the
2.HC-ranked
Tour of Hainan. It was followed by more victories in China: at the
2.1-ranked
Tour of Taihu Lake, Mareczko won all seven of the nine stages to end in bunch sprints. He also won the general classification, the points classification and the young rider classification. He was named in the start list for the
2016 Giro d'Italia, but abandoned the race on Stage 5.
Post-Southeast (2019–present) In October 2020, he was named in the startlist for the
Vuelta a España, recording a best stage finish of third place on the fourth stage. The following month, he signed a two-year contract with the team, from the 2021 season. However, folded at the end of the 2021 season, and Mareczko joined for the 2022 season. At the
2022 ZLM Toer Mareczko won the bunch sprint for Stage 2 however, he was relegated soon after and
Olav Kooij named as the winner. Mareczko won the following day's stage into , and ultimately finished the race second overall, behind Kooij. ==Major results==