BackgroundBrown Buttabean Motivation (BBM) is an organization providing support for Pacific people and Indigenous Māori to manage their weight, mainly through community-based exercise sessions and social support. It was started by DL, a man of Samoan and Māori descent, following his personal weight loss journey from a peak weight of 210 kg to less than half that amount. DL is a charismatic leader with a high media profile who is successful in soliciting donations from corporations in money and kindness. Over time, BBM’s activities have evolved to include healthy eating, food parcel provision, and other components of healthy living. A co-design team of university researchers and BBM staff are evaluating various components of the program and organization.ObjectiveThe purpose of this study is to build culturally centered system dynamics logic models to serve as the agreed theories of change for BBM and provide a basis for its ongoing effectiveness, sustainability, and continuous quality improvements.MethodsA systems science approach will clarify the purpose of BBM and identify the systemic processes needed to effectively and sustainably achieve the study’s purpose. Cognitive mapping interviews with key stakeholders will produce maps of their conceptions of BBM’s goals and related cause-and-effect processes. The themes arising from the analysis of these maps will provide the initial indicators of change to inform the questions for 2 series of group model building workshops. In these workshops, 2 groups (BBM staff and BBM members) will build qualitative systems models (casual loop diagrams), identifying feedback loops in the structures and processes of the BBM system that will enhance the program’s effectiveness, sustainability, and quality improvement. The Pacific and Māori team members will ensure that workshop content, processes, and outputs are grounded in cultural approaches appropriate for the BBM community, with several Pacific and Māori frameworks informing the methods. These include the Samoanfa’afaletuiresearch framework, which requires different perspectives to be woven together to create new knowledge, andkaupapa Māori–aligned research approaches, which create a culturally safe space to conduct research by, with, and for Māori. The Pacificfonofaleand Māorite whare tapa whāholistic frameworks for interpreting people’s dimensions of health and well-being will also inform this study.ResultsSystems logic models will inform BBM’s future developments as a sustainable organization and support its growth and development beyond its high dependence on DL’s charismatic leadership.ConclusionsThis study will adopt a novel and innovative approach to co-designing culturally centered system dynamics logic models for BBM by using systems science methods embedded within Pacific and Māori worldviews and weaving together a number of frameworks and methodologies. These will form the theories of change to enhance BBM’s effectiveness, sustainability, and continuous improvement.Trial RegistrationAustralian New Zealand Clinical Trial Registry ACTRN 12621-00093-1875; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=382320International Registered Report Identifier (IRRID)PRR1-10.2196/44229