Born in Żabokrzycz, in Podolia. In 1885-1886 he studied embryology and comparative anatomy in Lviv, and in 1888-1891 - philosophy and philology at the University of Geneva. Besides, he also completes studies in psychology in Paris and Leipzig. In 1893, together with Roman Dmowski, he founded the National League and later the National-Democratic Party (SND). From 1912 he was an editor of “Myśl Polska”. In 1909-1912 he was a deputy to the Third Imperial Duma, and in 1915-1918 – a member of the secretariate of the Interparty Political Circle. In 1916-1917 he also served on the Provisional Council of State. In the interwar period he engaged in political, and publicist, activity. In 1919 he held a seat in the Legislative Sejm, and was a senator in 1922-1935. He represented the Polish Senate at the celebrations of the septcentenary of the establishment of universities in Naples (1924) and Perugia (1925). Expert in, and propagator of, Benito Mussolini’s fascism, Jabłonowski was awarded the Commander’s Cross of the Italian Order of Saint Maurice and Lazarus. During the Second World War he lived in Warsaw, and then settled down in Sopot after the end of hostilities. He is the author of numerous studies and essays on Polish, and European, culture. His works were published in, among others, “Myśl Polska”, “Myśl Narodowa”, “Gazeta Warszawska”, “Głos”, and “Tygodnik Ilustrowany”. He also wrote the following books: Amica Italia (1926), Mowy Mussoliniego (1927), and Z biegiem lat 1890-1939. Wspomnienia o Romanie Dmowskim (1939).