This article contributes to understanding the conditions of socio-ecological change by focussing on the agency of individuals in the pathways to institutionalization. Drawing on the case of the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) and following the research program put forward by Westley et al. (2013), it addresses institutional entrepreneurship in an emerging environmental science-policy institution (ESPI) at a global scale. Drawing on ethnographic observations, semi-structured interviews, and document analysis, we propose a detailed chronology of the genesis of the IPBES before focussing on the final phase of the negotiations toward the creation of the institution. We analyze the techniques and skills deployed by the Chairman during the conference to handle the tensions at play in order both to prevent participants from deserting the negotiations arena and a lack of inclusiveness from discrediting the future institution. We stress that creating a new global environmental institution requires the situated exercise of an art of “having everybody on board” through techniques of inclusiveness which we characterize. Our results emphazise the major challenge of handling the fragmentation and plasticity of the groups of interest involved in the institutionalization process, thus adding to the theory of transformative agency of institutional entrepreneurs. While inclusiveness might remain partly unattainable, such techniques of inclusiveness appear to be a major condition of the legitimacy and success of the institutionnalization of a new global ESPI. Our results also add to the literature on boundary-making within ESPIs by emphazising the mutiplicity and plasticity of the groups actually at stake and further complicating the model of ‘Landscape of Tensions’ proposed by Parker and Crona (2012).