After his high school graduation (passed as an extramural exam) in 1939 he enlisted in the Junior Labor Corps, and his stay in their ranks at the construction of fortifications near Wizna was interrupted by the outbreak of war. He himself, working first in accounting and then physically as a porter and coachman, survived the war, but his parents were not so lucky. In May 1940, the Gestapo arrested Stanisław Mróz, who had a number of anti-fascist publications on his account. The artist’s father died in the Auschwitz-Birkenau extermination camp less than a year later, whilst Barbara Mróz died in her own home even earlier, on Christmas Eve 1940.
In 1947, Mróz began studying graphic design and set design at the Academy of Fine Arts in his native Kraków, to which he returned after a brief stay in Germany, remaining in his hometown for the rest of his life. At the academy, he met his future wife, textile art student Alina Nieniewska, as well as one of the key figures in his artistic career – Marian Eile, the legendary editor of Przekrój, who was a lecturer at the Faculty of Stage Design. It was at university that Eile noticed Mróz’s talent and, whilst the latter was still a student, invited him to join the Przekrój team – as a draughtsman, and later as a creator of the entire graphic design. In the editorial team of Przekrój, Mróz became one of the pioneers of a close connection between illustrations and typography, which was expressed, amongst other things, in the tables of contents prepared for each issue. Mróz collaborated with the magazine to the end of his life, simultaneously creating illustrations for a number of other titles, such as the tabloid Ty i Ja, Życie Literackie, Polski and the youth magazine Zebra.