He currently plays for Unia Skierniewice, wearing the number 18 shirt. He plays primarily as a Forward.

His most recent move was a Free from MKS Notec Czarnkow to Unia Skierniewice on 2026-01-31. The reported fee was 0.005M €.

In the Poland Liga 2 2025-2026 season, Jan mierzwa scored 0 goals and provided 0 assists across 1 appearances, averaging 0 goals per game with 0 shots attempted and 0 on target.