His lectures on Polish history created great enthusiasm, as shown in some lines addressed to him by Adam Mickiewicz that led to Lelewel's removal by the Russians in 1824.

[3] In 1847, he, together with Karl Marx and Friedrich Engels, became a founding member and Vizepräses (vice president) of the Demokratische Gesellschaft zur Einigung und Verbrüderung aller Völker (Democratic Society for Unity and Brotherhood of All Peoples), seated in Brussels.

[4] His historical works were popular in Ukraine especially among members of the Ruthenian Trinity and the Brotherhood of Saints Cyril and Methodius (particularly historian Mykola Kostomarov).

His method is shown in the "little history" of Poland, first published at Warsaw in Polish in 1823, under the title Dzieje Polski, and afterwards largely rewritten in the Histoire de Pologne (2 vols., 1844).

While employed in the Warsaw University library, he studied bibliography, and the fruits of his labors may be seen in his Bibliograficznych Ksiąg dwoje (Two Bibliographic Books, 2 vols., 1823–1826).

[4] Lelewel wrote an autobiography (Adventures while Prosecuting Researches and Inquiries on Polish Matters), printed in his Polska (Poland).