Mieciel was born on December 22, 1975 in Gdynia, Poland. He played for several clubs in his native country (Wisla Tczew, Lechia Gdansk, Hutnik Warsaw, Legia and Lodski) before playing abroad for Borussia Moechengladbach in 1996. He returned to Poland and Legia, for the 2002 season and, in the summer of that year, Mieciel came to Greece to play for Iraklis Thessaloniki. He recorded 16 goals in 64 appearances for Iraklis before transferring to PAOK in 2005.
Mieciel has since played in Germany with Vfl Bochum and in his native Poland.