[6] In 1991, Zalewski was elected to the Sejm as a Democratic Union party member in the 26 Siedlce electorical district.

[3] He was elected again on 25 September 2005 as part of the Law and Justice platform with 14,068 votes in the 11 Sieradz district.

[12][13] Despite being the party's vice president, he left Law and Justice in 2007 along with fellow member Kazimierz Ujazdowski after an argument with former Prime Minister Jarosław Kaczyński.

[14][15] He joined the Civic Platform (PO) in 2009[16] and was a member of the European People's Party Group by 2012.

[24][12] The ejection occurred after Zalewski and Raś signed a letter along with several senators and 49 other MEPs from PO and KO calling for a change in leadership within the coalition.

[16][25][26] Both appealed their respective removal,[27] which the PO defended by criticizing Zalewski for sharing his contrary opinions with the media but refusing to speak up during diplomatic meetings during his years as a Sejm member.