During years of the secondary school, he collaborated with the mathematical journal for secondary school students Középiskolai Matematikai Lapok, and won the national Eötvös Loránd Mathematical Competition. He enrolled to the Technical University of Budapest as a student of chemical engineering, but in the same year he moved on to the University of Budapest, and after a year to the University of Göttingen. His doctoral research was supervised by Hilbert graduating in June 1909. His 49-page thesis studies systems of Sturm–Liouville functions and spherical functions, introducing the now widely used Haar orthogonal systems. In the same year he habilitated to become a private professor of the university.
In 1912, the Franz Joseph University in Kolozsvár, Austria-Hungary (now Cluj-Napoca in Romania) invited him along with Gyula Farkas and Frigyes Riesz to join as faculty, and he became the professor of 'Quatitics'. A number of his lecture notes from the time became established books later. After the Treaty of Trianon, which ceded Transylvania to Romania, the university had to move to Szeged, the closest city within the new boundaries, where he with Riesz established the Centre of Mathematics, and the first internationally recognised Hungarian mathematical journal, the Acta Scientiarum Mathematicarum.
