Mięciel started his football career at Wisła Tczew for which he played until 1990. The next stop in his career was Lechia Gdańsk. In December 1993 he transferred to Hutnik Warszawa but after only six months he moved on to local rivals Legia Warszawa where he played until 2001 (only interrupted by a half year loan to ŁKS Łódź in 1995).
After a disappointing season at Borussia Mönchengladbach Mięciel went on to Greece. His first stop was Iraklis Saloniki. After three seasons he moved to local rivals PAOK Thessaloniki FC. In his first season he scored in five times in 13 matches. In the next season he scored five goals in 25 matches. His most successful season was 2006/2007: in 27 matches he notched 14 goals. He was one of the topscorers in the Greek league and PAOK's "most valuable player" of that season.