A leading figure of the Conservatives for the following years, he held several ministerial positions after 1891: he was Minister of Religious Affairs and Education in the Lascăr Catargiu cabinet (1891–1895) and again under Gheorghe Grigore Cantacuzino (April 1899 – January 1900), as well as Minister of Finance (January–July 1900; 1904–1907) in both Cantacuzino cabinets. In 1899, Ionescu took the side of Jewish scientist Lazăr Şăineanu, endorsing his naturalization in front of opposition from the antisemitic faction among the National Liberals, and helped bring the matter for renewed discussion in the Senate. He also helped the scholar earn credentials by overseeing his conversion from Judaism to the Romanian Orthodox Church, and serving as his godfather. However, by the end of the same year, Ionescu had mysteriously changed in mind: he voted in favor of complicating naturalization procedures for Jews and, as Education Minister, stripped Şăineanu of his honorary teaching position within the University of Bucharest. A supposed atheist, he was criticized by the opposition for favoring an increased role for the Romanian Orthodox Church, and replied that it was a matter for his own conscience. During the period, he befriended the notorious and independent-minded dramatist Ion Luca Caragiale, who later supported his dissident politics.