Global constitutionalism offers a utopian picture of the future of international law. Its advocates suggest a governance system is emergent that will fill the gaps in legitimacy, democracy and the rule of law present in international law. Speculation about the future of international law is shaped, partly at least, by global constitutionalism aspiring to create a better global legal order, by filling these legitimacy gaps with both normative and procedural constitutionalism. But this raises the question ‘better for whom’? Feminist theory has challenged the foundations of both international law and constitutionalism; demonstrating that the design of normative structures accommodates and sustains prevailing patriarchal forms that leave little room for alternative accounts or voices. Both international and constitutional law’s structures support the status quo and are resistant to critical and feminist voices. The question is whether it is possible for constitutionalism to change international law in ways that will open it up to alternate possibilities. Building on a seven-point manifesto of feminist constitutionalism, previously proffered by the authors, which inculcated feminist concerns into global constitutionalism, this article offers an alternative starting point: feminist science fiction. Feminist utopian tracts such as Charlotte Perkins Gilman’s Herland and Ursula K Le Guin’s The Left Hand of Darkness offer valuable lessons for global constitutionalist discourses. The article uses feminist utopias in science fiction to better understand how to dismantle hierarchical structures, how to build feminist societies, and how to find approaches to governance not predicated on patriarchy. It does so by focusing on feminist alternatives for constructing communities, for understanding constituent power and constituent moments, and dismantling manifestations of the public/private divide. This article demonstrates that reading feminist utopian science fiction facilitates the reimagining of global constitutionalism.