Leśniewski was born on 28 March 1886 at Serpukhov, near Moscow, to father Izydor, an engineer working on the construction of the Trans-Siberian Railway, and mother Helena (née Palczewska).

Together with Alfred Tarski and Jan Łukasiewicz, he formed a trio which made the University of Warsaw, during the interbellum, perhaps the most important research center in the world for formal logic.

A good textbook presentation of these systems is that by Simons (1987), who compares and contrasts them with the variants of mereology, more popular nowadays, descending from the calculus of individuals of Leonard and Goodman.

He pointed to Russell's paradox and the like in support of his rejection, and devised his three formal systems as a concrete alternative to set theory.

Even though Alfred Tarski was his sole doctoral pupil, Leśniewski nevertheless strongly influenced an entire generation of Polish logicians and mathematicians via his teaching at the University of Warsaw.