Schlick was born in Berlin to a wealthy family. He studied physics at Heidelberg, Lausanne, and, ultimately, the University of Berlin under Max Planck. In 1904, he completed his dissertation essay, "Über die Reflexion des Lichts in einer inhomogenen Schicht" ("On the Reflection of Light in a Non-Homogeneous Medium"). In 1908, he published Lebensweisheit ("The Wisdom of Life"), a slim volume about eudaemonism, the theory that happiness is the highest ethical pursuit. His habilitation essay, "Das Wesen der Wahrheit nach der modernen Logik" ("The Nature of Truth According to Modern Logic"), was published in 1910. Several essays about aesthetics followed, whereupon Schlick turned his attention to problems of epistemology, the philosophy of science, and more general questions about science. In this last category, Schlick distinguished himself by publishing a paper in 1915 about Einstein's special theory of relativity, then only ten years old. He also published Raum und Zeit in der gegenwärtigen Physik ("Space and Time in Modern Physics"), a more systematic treatment of post-Newtonian physics.
In 1922, Schlick became a professor in the philosophy of inductive sciences at the University of Vienna after two unsatisfying appointments in Rostock and Kiel. In the same year occurred two events that shaped the remainder of Schlick's life. First, a group of philosophers and scientists (including but not limited to Rudolf Carnap, Herbert Feigl, Kurt Gödel, Hans Hahn, Otto Neurath, and Friedrich Waismann) suggested to Schlick that they conduct regular meetings to discuss science and philosophy. They initially called themselves the Ernst Mach Association, but forever after they have been known as the Vienna Circle. The second great event of 1922 was the publication of Ludwig Wittgenstein's Tractatus Logico-Philosophicus, a work of terse, lapidary brilliance that advanced, among other things, a logical theory of symbolism and a 'picture theory' of language. Schlick and his group were overwhelmed by the work: they made it a topic for discussion at nearly every meeting. Schlick himself contacted Wittgenstein in 1924 and extolled the virtues of Wittgenstein's book vis-a-vis his immediate circle. Eventually Wittgenstein agreed to meet with Schlick and Waismann to discuss the Tractatus and other ideas. Through Schlick's influence, Wittgenstein was encouraged to consider a return to philosophy after some ten years of idleness. It is partly to Schlick's credit that Wittgenstein began to pen the reflections that make up large parts of Philosophical Investigations. Schlick and Waismann's discussions with Wittgenstein continued until the latter felt that germinal ideas had been used without permission in an essay by Carnap. Wittgenstein continued discussions in letters to Schlick, but his formal association with the Vienna Circle ended in 1932.
Schlick had worked on his Allgemeine Erkenntnislehre (General Theory of Knowledge) between 1918 and 1925, and, though later developments in his philosophy were to make various of his epistemological contentions untenable, the General Theory is perhaps his greatest work in its acute reasoning against synthetic a priori knowledge. Between 1926 and 1930, Schlick labored to finish Fragen der Ethik (Problems of Ethics), in which he surprised some of his fellow Circlists by including ethics as a viable branch of philosophy. Also during this time, the Vienna Circle published The Scientific View of the World: The Vienna Circle as an homage to Schlick. Its strong anti-metaphysical stance crystallized the viewpoint of the group.
With the rise of the Nazis in Germany and Austria, many of the Vienna Circle's members left for America and the United Kingdom. Schlick, however, stayed on at the University of Vienna: when visited by Herbert Feigl in 1935, he expressed dismay at events in Germany. On June 22, 1936, Schlick was ascending the steps of the University for a class when he was confronted by a former student, Johann Nelböck, who drew a pistol and shot him in the chest. Schlick died very soon afterward. The student was tried and sentenced, but he became a cause célèbre for the growing anti-Jewish sentiments in the city. (That Schlick was not Jewish tended to be overlooked.) In a fitting and grotesque twist of fate, Nelböck was paroled shortly afterward and became a member of the Austrian Nazi Party after the Anschluss.
Schlick's enduring contribution to the world of philosophy is as the fount of logical positivism. His humanity, good will, gentleness, and especially his encouragement have been documented by many of his peers. Herbert Feigl and Albert Blumberg, in their excellent introduction to "General Theory of Knowledge," have written, "No other thinker was so well prepared to give new impetus to the philosophical questings of the younger generation. Though many of his students and successors have attained a higher degree of exactitude and adequacy in their logical analyses of problems in the theory of knowledge, Schlick had an unsurpassed sense for what is essential in philosophical issues." (Feigl and Blumberg, "Introduction," General Theory of Knowledge, p. xxi).