To address the prevalence and complexities of sustainable development challenges around the world, organizations in the business, government, and non-profit sectors are increasingly collaborating via multi-stakeholder partnerships. Because complex problems can be neither understood nor addressed by a single organization, it is necessary to bring together the knowledge and resources of many stakeholders. Yet, how these partnerships coordinate their collaborative activities to achieve mutual and organization-specific goals is not well understood. This study takes an organization design perspective of collaborative decision-making processes to explore how they impact the effectiveness of multi-stakeholder partnerships. We compare the decision-making processes of 94 sustainability-focused multi-stakeholder partnerships and find that collaborative decision-making has an indirect and positive impact on partnership capacity through systems that keep partners informed, coordinate partner interactions, and facilitate ongoing learning. The implications of this study for multi-stakeholder partnership research and practice are that partnership capacity is contingent on the design of decision-making processes, as well as internal mechanisms that coordinate and monitor collaborative activities. © 2018 Springer Science+Business Media B.V., part of Springer Nature