Diversity has long been recognized as a critical component of collaborative governance. Among many rationales, the representation of diverse perspectives and participants in collaborative governance arrangements is expected to facilitate holistic understandings of complex public policy and management issues while promoting principles of democracy and inclusion. Such outcomes, however, are typically only achievable if the process of collaboration similarly engenders these principles. In this article, we investigate the dynamic relationship between diversity and perceived procedural justice in the context of 10 collaborative policymaking groups involved in guiding U.S. marine aquaculture policy development. Among our key findings is that certain types of participant diversity (i.e., affiliation and intergovernmental diversity) and diversity in beliefs about science and local knowledge are significantly associated with perceptions of procedural justice among participants within the collaborative groups. We also find that the relationship between participant diversity and perceived procedural justice is curvilinear; the positive effect of diversity is highest when the level of diversity is moderate (an inverted U-shaped pattern). We conclude our article with practical implications and suggestions for future research on procedural justice within collaborative partnerships.