This article offers a novel foray into international mindedness and posthuman theory. International mindedness underpins the International Baccalaureate's aim to achieve a better and more peaceful world. However, in a global context of planetary emergency and widening inequalities, it seems imperative to rethink international mindedness within a posthumanist frame, that is, beyond anthropocentric notions of education that privilege human exceptionalism. The reconceptualization of international mindedness as relational becoming is illuminated through five theoretical propositions which are illustrated empirically using 'material moments'. Relational becoming rejects mind and body binaries, affirms nonhuman-human assemblages, enables distributed agency, enacts ethics of response-ability and engages with past and present entanglements. 'Posthumanizing' international mindedness, through the concept of relational becoming, prompts more nuanced insights into educational privilege, nation-states, globalism and enduring colonialist inheritances.