International society debates help us theorize how states or non-state actors matter for the organization of international relations but pay less attention to actors that transcend the state/non-state binary, and especially how contested states that lack recognition and are excluded from international society have engaged with its norms and institutions, particularly in a collective fashion. In order to explore this, we focus on the Unrepresented Nations and Peoples Organization (UNPO), which has been seen as showing a tension between mimicry of the international system and opening new directions and we explore how has the UNPO engaged with international society norms on statehood and to what extent its structures mirror those of other international organizations. We compare the UNPO to other organizations, and we analyze a set of original data, and we find that the UNPO resembles organizations of international society, but it is also a space where international norms are not altogether rejected but “re-imagined,” for example, in ways that seek to strengthen the credentials of contested states. Simultaneously, the purpose of UNPO membership for contested states is to eventually cease to exist, when they join international society, which testifies to the legitimacy that UNPO gives to international society. Thus, our study cross-fertilizes the themes of contested statehood, international society, and the UNPO to offer a missing account of the collective agency of contested states in engaging with international society, which also contributes to debates on international relations from apparently marginal actors.