Errol E. Harris devoted his life to grappling with the big questions concerning the relationship between nature and mind. Harris’s career was distinguished, his works were widely published, and yet his metaphysics has until now been excluded from mainstream discourse. The purpose of this work is to outline Harris’s philosophies of nature, mind, and science so as to provide his overarching metaphysics a rigorous and sympathetic assessment. This thesis begins with an examination of Harris’s biography, including key inspirations that led to the development of his philosophical system. In the remaining three parts I compare Harris’s distinctive phenomenological and interdisciplinary approach to the hard problem of consciousness with his closest theoretical analogues in the contemporary philosophies of physics, biology, and mind. I argue that Harris’s metaphysics both anticipates and provides a means of unifying the theories of Bohmian quantum mechanics, systems evolution, and 4E cognition. Specifically, I contend that when clarified by the philosophical developments of systems theory, Harris’s metaphysics reveals as yet unnoticed implications of autopoietic enactivism for a novel version of the anthropic cosmological principle. I conclude that insofar as the resulting metaphysics of “dialectical holism” remains consistent, it provides both methodological and theoretical principles towards revising neutral monism and naturalizing phenomenology.