After the outbreak of World War II, Boy-Żeleński moved to Soviet-occupied Lwów, where he stayed with his wife's brother-in-law.
In Lviv, Boy joined the Soviet-led University as the head of the Department of French Literature.
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 USSR and the Soviet-held Polish Kresy, Boy remained in Lwów (now Lviv, Ukraine).
The city was captured on the night of 4 July 1941; he was arrested and taken to the Wulka hills where he was murdered for being "a Soviet spy", together with 45 other Polish professors, artists and intelligentsia in what became known as the massacre of Lviv professors.
After the outbreak of World War II, Boy-Żeleński moved to Soviet-occupied Lwów, where he stayed with his wife's brother-in-law. In Lviv, Boy joined the Soviet-led University as the head of the Department of French Literature. 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 USSR and the Soviet-held Polish Kresy, Boy remained in Lwów (now Lviv, Ukraine). The city was captured on the night of 4 July 1941; he was arrested and taken to the Wulka hills where he was murdered for being "a Soviet spy", together with 45 other Polish professors, artists and intelligentsia in what became known as the massacre of Lviv professors.
Tadeusz Boy-Żeleński