The Western Lake Erie Basin (WLEB) faces ongoing challenges with adoption and sustained use of conservation practices across agricultural landscapes to reduce nutrient pollution. Despite substantial investments in incentive programs for conservation adoption, long-term adoption rates lag due to complex social, behavioral, and economic barriers. To address this problem, the National Wildlife Federation and University of Michigan Water Center engaged a broad group of conservation partners to co-develop a Theory of Change (ToC) model for the WLEB. The ToC model is a powerful tool for developing an actionable roadmap to leverage new and existing conservation programs, coordinate outreach and technical service, address adoption barriers through program evaluation, and map connections between activities, intermediate outcomes, and long-term goals. This process convenes an inclusive conservation stakeholder group to encourage alignment and effective coordination across various efforts and organizations. Through the consolidation of shared assumptions and goals between WLEB actors, participants helped develop pathways to improve direct communication with farmers, identify implementable evaluation strategies and key indicators of success, and structure programs around the most feasible and impactful strategies for expanding conservation adoption. This study presents the WLEB ToC roadmap and its intermediate outcomes and evaluates the ToC process on a watershed-scale.