This paper seeks to reinterpret the life and work of J.B.S. Haldane by focusing on an illuminating but largely ignored essay he published in 1927, "The Last Judgment" - the sequel to his better known work, Daedalus (1924). This astonishing essay expresses a vision of the human future over the next 40,000.000 years, one that revises and updates Wellsian futurism with the long implications of the "new biology" for human destiny. That vision served as a kind of lifelong credo, one that infused and informed his diverse scientific work, political activities, and popular writing, and that gave unity and coherence to his remarkable career.