This thesis interprets the work of the German jurist and state theorist Carl Schmitt through the lens of a ‘double-historicism’ by using unpublished archival materials – journal entries, letters, manuscripts, and marginalia. Not only were Schmitt’s ideas and writings shaped by his intellectual and political context, but he himself viewed legal and political concepts as historically contingent. The first chapter reconstructs the ‘canonization’ of Carl Schmitt in the field of political theory, focusing on the reception and sanitization of his work in English language scholarship. The second chapter excavates Schmitt’s concept of ‘historicity’ and his turn to the founder of the Historical School of Law, Friedrich Carl von Savigny, in lectures given in 1943 and 1944. I then argue this historical turn is the key to understanding Schmitt’s postwar work, connecting four major monographs published concurrently in 1950. The following chapters show how Schmitt mobilizes historicity as a critique of natural law theories and the right of resistance against tyrannical regimes (chapter 3), the appropriation of Scholastic just war doctrines in the postwar period (chapter 4), Marxism’s weaponization of legality (chapter 5) and utopianism as a form of annihilation of law and the ‘de-localization’ of both nature and man (chapter 6). Schmitt saw both legal positivism and natural law theories as posing an existential crisis to the future of jurisprudence, one that could only be overcome by recourse to a self-reflexive history of the discipline.