<p>This article examines the tension between inclusion and exclusion in collaborative governance arrangements in high-conflict settings. Collaborative governance scholarship recognizes the paradoxical existence of inclusionary and exclusionary mechanisms, yet little is known about how collaborations manage – and are affected by – this tension, particularly in a setting of conflict that puts the tension to the test. Relying on material from 49 in-depth interviews with key stakeholders and 5 focus groups, we study the case of the Future Alliance, an ambitious collaborative governance arrangement surrounding the multibillion-euro Oosterweel project in Antwerp (Belgium). The Alliance sought to bring together governmental and civil society actors as equal decision-making partners after decades of entrenched conflict. We conclude that efforts made in the name of promoting collaborative inclusion, such as designing flexible procedures, simultaneously led to exclusion. Rather than opening up the space for conflict within the collaborative process, these mechanisms narrowed it, leaving many participants disillusioned. While collaborative governance helped break a policy deadlock and move toward decision-making and implementation, its failure to address exclusionary effects risks undermining the very promises it makes.</p>