Rządkowski was born on 14 July 1860 in Belsk Duży in the Warsaw Governorate of Congress Poland, to an old gentry family owning a number of villages and manors in the area of Łomża.

Originating from the regions of Podlaskie and Kurpie, following the November Uprising the family was forced to move to central Poland, where Rządkowski was born.

Because of that in 1915 the tsar nominated him to the post of the commanding officer of the Puławy Legion and then the Polish Rifle Brigade, the first entirely-Polish units formed in Russia since the January Uprising half a century before.

Rządkowski was a skilled commander, but also had to become a politician in order to convince Nicholas II to extend the Polish formations fighting alongside the Russian Army.

Promoted to the rank of Lieutenant General, he became the commanding officer of the 1st Lithuanian-Belarusian Division, a unit formed mostly of Poles living in the areas broadly referred to as Kresy.