In the early 20th century, Sadowski studied mechanics at the Lviv Polytechnic, and there he got in touch with Polish independence movement.

In 1919 he entered the Polish Army Headquarters' School in Warsaw, then was sent on a two-year course to Ecole Superieure de Guerre in Paris.

On 19 March 1939 Sadowski was promoted to general, and took command of the freshly created Fortified Area of Silesia.

During the opening phase of the Second World War, the Invasion of Poland, he was commandant of the Operational Group Silesia, which was part of the Kraków Army.

Sadowski's troops participated in the defence of Kraków, then fought in the area of Kielce and finally, in the Battle of Tomaszów Lubelski, where they were defeated.