 He was a member of the liberal Kalisz Opposition ("Kaliszanie") in the parliament since 1820; the group was named after the voivodeship which he and his brother, Wincenty Niemojowski, both notable members of the group, were from.In 1821 married Bonawentura Wiktoria Lubowidzka, with whom he had two children.In the Sejm, Bonawentura soon became a major nuisance to the Russian officials.