After the suppression of the uprising, he emigrated to Paris, where he was a member of the "Polish Deputation" (Deputacja Polska),[1] an independence organization that arose in Paris in 1795 (remaining active till 1796) and grouped representatives of the Polish émigré radical wing.

The Polish Deputation hoped to bring about an armed uprising and social revolution in occupied Poland with the support of revolutionary France.

[2] The Polish Deputation thereby came into conflict with the moderate Kościuszko-Uprising émigré activists of the "Agency" (Agencja), founded in Paris in 1794, which opposed armed action in Poland, counting instead on France's diplomatic and military aid, and supporting Henryk Dąbrowski's Polish Legions.

[3] On returning to Warsaw during the Prussian occupation, Szaniawski co-edited Gazeta Warszawska (The Warsaw Gazette) and initiated "Korespondencja w materiach obraz kraju i narodu polskiego rozjaśniających" ("Correspondence on Matters Elucidating the Picture of Poland and the Polish People").

He had entered the civil service and rose quickly to high station, becoming attorney general of the Duchy of Warsaw (1807–15), then secretary of the Provisional Government, then referendary of state under the Congress Poland.