 In 1915 the fortunes of war put Germany in control of Warsaw, and they decided to re-open the university, which had not been allowed to function as a Polish-speaking university under Russian rule. Łukasiewicz became professor of philosophy there. In 1916 he was dean of the Faculty of Arts, and in 1917 prorector of the university. In 1918 he left the university, being appointed Head of the Department of Higher Schools in the new Polish Ministry of Education, and after Poland obtained full independence he became Minister of Education in Paderewski’s Cabinet, serving from January to December 1919. From 1920 until 1939 he was, as was Leśniewski, a Professor in the Faculty of Natural Sciences at the University of Warsaw. In 1922/23 and again in 1931/32 he served as rector of the university. In 1929 he married Regina Barwińska.