From the physical, mathematical, and conceptual points of view, Roger Joseph Boscovich’s original 1758 formulation of the principle of physical determinism and Pierre-Simon Laplace’s later 1814 rendering of the principle appear identical. Both Boscovich and Laplace expressed epistemological and ontological commitments to the ideas that (a) the present state of the universe is a necessary effect of its preceding states and the immediate cause of the states that follow, and (b) that knowledge of the present state of the universe allows the full knowledge of its future and past states. However, their respective metaphysical readings of the principle of determinism radically differ. Contrary to the secularized reading of the principle given by Laplace, Boscovich’s reading of the principle strongly affirms the natural theology he inherited from Newton. In particular, in addition to enhancing the traditional teleological and cosmological arguments for the existence of God based on probability theory and his specific views of the nature of infinity, Boscovich also offered an innovative version of the cosmological argument based on the very principle of physical determinism he was the first to formulate. The purpose of this article is to analyze the content and context of these metaphysical differences between Boscovich and Laplace in respect to the principle of physical determinism, which nevertheless leave intact the scientific content of the principle.