In October 2006, he was appointed manager of Ekstraklasa side Zagłębie Lubin, leading the club to the 2006–07 league title.

After defeating Portugal in the play-offs, Poland under his leadership qualified for the first time since 1994 for the final tournament of the 2019 UEFA European Under-21 Championship.

[8] On 28 April 2021, Michniewicz won his second Polish Championship after 0–0 draw between Jagiellonia Białystok and Raków Częstochowa (as the latter team had already lost mathematical chances of catching up with Legia), with three games to spare.

[9] On 26 August 2021, Legia led by Michniewicz defeated SK Slavia Prague, and for the first time in five years qualified for the group stages of a European cup.

After four consecutive defeats, managing nine points in ten fixtures and sitting 15th in the table,[13] Michniewicz was dismissed on 25 October 2021.

[27] Following a good start to his stint, Abha suffered four straight league defeats in September, which led to Michniewicz's dismissal on 1 October 2023.

[30] On 15 October, with a record of four wins, three draws and two losses across all competitions, Michniewicz and AS FAR agreed to mutually part ways.

[31] Michniewicz was born in Byarozawka, then in the Byelorussian SSR, Soviet Union (present-day Belarus), while his mother was visiting her family; but grew up in Biskupiec, Poland.