On 29 October 1938, Kossowski married Stefania Szurlej, whom he had met in Rome. He was named "senior assistant" at the Warsaw Academy of Art and won first prize in a competition to create interior sgraffito work at Warsaw's Central Railway Station. But this project was abandoned after Germany invaded Poland in September 1939. Kossowski's wife fled with her parents; and Kossowski himself went east, where he was arrested by invading Russian troops in November 1939.