The judgment of the Supreme Court of Canada in the Quebec Secession Reference has produced a torrent of public commentary. Given the fundamental issues about the relationship between law and politics raised by the judgment, what is remarkable is that that commentary has remained almost entirely in a pragmatic perspective, which asks how positive politics entered into the motivations and justifications of the Court, and looks at the results in terms of their political consequences, without deep or sustained reflection on the ultimate grounds for the role the Court took upon itself, or on the normative sources of its reasoning. In this article, we explore the Quebec Secession Reference through the lens of constitutional theory. In particular, we highlight three unconventional aspects of the Court’s reasoning: (a) the supplementation of the written constitution through an explicit process of amendment-like interpretation to craft a new legal framework governing the secession of a province from Canada, (b) the vesting by the Court of substantial, if not exclusive responsibility for interpreting the constitutional rules on secession in particular situations or contexts with political organs, not the courts, and (c) the ascent by the court to abstract normativity, in articulating a normative vision of the Canadian constitutional order, whence it derived the legal framework governing secession. In addition to drawing attention to these unusual aspects of the judgment, we articulate the theoretical justifications that both explain and justify those features of the judgment, and identify issues for future discussion.