Background: Despite the evident trend in health research to emphasise co-production approaches, there is a lack of established, comprehensive and concrete strategies and evaluation methods to effectively guide and assess them. This project aimed to develop, validate, and test a toolkit designed to enhance and evaluate co-productions in mental health research. The toolkit includes practical evaluation tools, such as a structured questionnaire and tailored interview guides, to support the initiation of research projects and assess the involvement, process and impact of co-production efforts. Methods: This project used a co-production approach with formative research design to develop a comprehensive toolkit for evaluating the process and impact of co-production in mental health research. Conducted between 2022 and 2024, the project involved iterative engagement with diverse stakeholder groups, providing a dynamic testbed for developing, validating, and field-testing the instruments. The paper outlines the four-phase process: (1) toolkit generation, (2) validation, (3) field-testing, and (4) completion, detailing how the co-production approach shaped the toolkit’s design, relevance, usability, and rigor. Results: The result of this project is a structured, practical, and comprehensive co-production evaluation toolkit designed specifically for mental health research, potentially involving a wide range of partnerships. The toolkit includes a project initiation guide, a process-oriented survey and interview-guide for mid- and post-project evaluations, and an impact-focused post-project group interview guide. Conclusions: The findings address a critical gap in mental health research by developing a structured, practical, and comprehensive co-production evaluation toolkit. The toolkit offers comprehensive strategies for evaluating involvement and both the processes and impacts of co-production throughout a project’s lifecycle. © The Author(s) 2025.