In 1929-1934, he studied philosophy at Lviv and Krakow universities. In 1930s, he became one of the leaders of Organization of Ukrainian Nationalists (OUN).
During World War II, at the beginning of the German-Soviet war, the OUN-B faction (headed by Stepan Bandera) proclaimed Ukraine's independence in Lviv on 30 June 1941, with Yaroslav Stetsko as a prime minister. After twelve days, all members of this government were arrested by Germans. Bandera and Stetsko were sent to Berlin and then into concentration camp Sachsenhausen-Zellenbau, where were held such political prisoners as Kurt Schuschnigg, Edouard Daladier, Stefan Rowecki, etc. Stetsko was kept there until December 1944, and was freed when Germans decided to form Ukrainian National Army led by general Pavlo Shandruk.
After World War II, he lived in Munich.