Zygmunt Zawirski, one of the members of the Lvov-Warsaw School, developed one of the earliest formal attempts to adapt logic to quantum mechanics in the early 1930s. Motivated by the view that the probabilistic and indeterministic character of quantum theory invalidates some of the laws of classical logic (specifically the law of excluded middle), he sought an alternative appropriate logical framework. At the same time, he participated in contemporary discussions concerning possible applications of the newly developed many-valued logic of Jan Łukasiewicz. Zawirski regarded quantum mechanics as a promising area for such an application. In this talk, I revisit Zawirski’s work and show that it should be regarded as the earliest historically documented system of quantum logic, preceding the more widely known proposal of Birkhoff and von Neumann. I will present the historical and philosophical background of his project and sketch the structure of his logical system. Furthermore, I will discuss how his treatment of many-valued logic as a logic of probability anticipates ideas that later became central in non-deterministic semantics - a topic of currently ongoing collaborative research. I will also briefly discuss related work by some of his contemporaries, including Stefan Mazurkiewicz and Hans Reichenbach, who offered alternative approaches to the relationship between many-valued logic and probability.