He wrote books and dramas. His best known work is the drama "Niemcy" (Germans) written in 1949. A left-wing activist before World World War II, he spent the war in the German Prisoner Of War camps.
After the war, he became a communist activist in People"s Poland.
In the years 1945–1948, he was a Deputy Minister of Culture and Artist He is recognized as having a significant influence on post-war Polish cultural policy.
While finishing his education in chemistry and technology, he published his first poems in or around 1918 and 1919. He moved to Silesia where he published his first poetry anthology, "Młoty nad światem" (Hammers over the world), in 1928 and his first novel, a "peasants response to Kordian of Juliusz Słowacki", entitled "Kordian i cham" (Kordian and the Boor) in 1932.
He also wrote left-wing leaning essays published in magazines, newspapers and brochures.
His later novels "Pawie pióra" (Peacock feathers) and "Sidła" (A trap) were less successful. After the German invasion of Poland, in which he fought in the Polish army as an officer, he was arrested and spent the war in a Prisoner Of War camp where he was an educational and cultural activist, organizing a theatre. Two of his novels, not finished before the invasion, were lost during the war.
After the war, he returned to his literary career, now writing more dramas for the theater.
His 1948 "Odwet" (Retribution) was well received, but it was his 1949 "Niemcy" (Germans), a drama addressing the issue of Germany"s moral responsibility for World World War II, that gained him international recognition, translated into 14 languages. He also became a political activist and politician.
He was an active and vocal supporter of the new communist order in Poland, actively involved in taking over and politicizing the post-war Polish culture, introducing the philosophy of socrealism (see socrealism in Poland). He is recognized as having a significant influence on post-war Polish cultural policy and being a major literary figure.
Afterwards, he became a full-time writer, moving back to Krakow and writing the first of his theatrical dramas "Bohater naszych czasów" (Hero of our times) in 1935, rewritten three years later as "Przygoda z Vaterlandem" (An adventure with Vaterland), both notable for their strong critique of Nazism.
Leon Kruczkowski has also held the following positions: Deputy to Polish parliament (Sejm) from 1946 to 1956 and member of the Polish Council of State from 1957. In the years 1945–1948, he was a Deputy Minister of Culture and Art, Deputy to Polish parliament (Sejm) from 1945 to 1956 and from 1957, a member of the Polish Council of State.