Because higher education in Polish was forbidden in Warsaw under Russian rule, in 1892 Żeleński left for Kraków, in Austrian-ruled Galicia, where he enrolled at the Jagiellonian University medical school.

The same year, he co-organised the famous Zielony Balonik ("Green Balloon") cabaret, which gathered notable personalities of Polish culture, including his brother Edward and Jan August Kisielewski, Stanisław Kuczborski, Witold Noskowski, Stanisław Sierosławski, Rudolf Starzewski, Edward Leszczyński, Teofil Trzciński, Karol Frycz, Ludwik Puget, Kazimierz Sichulski, Jan Skotnicki and Feliks Jasieński.

In the sketches, poems, satirical songs, and short stories that he wrote for Zielony Balonik, Boy-Żeleński criticized and mocked the conservative authorities and the two-faced morality of the city folk, but also the grandiloquent style of Młoda Polska and Kraków's bohemians.

Criticized by many for his public and frequent collaboration with the Soviet occupation forces, he maintained contacts with many prominent professors and artists, who found themselves in the city after the Polish Defensive War.

He also took part in creating the Communist propaganda newspaper Czerwony Sztandar ("Red Banner") and became one of the prominent members of the Society of Polish Writers.

After Nazi Germany broke the German–Soviet treaty and attacked the Soviet Union and the Soviet-held Polish Kresy, Boy remained in Lwów (now Lviv, Ukraine).