Abstract Background Every urban slum creates challenges too complex for governments to resolve when working alone. Old Fadama, the largest slum in in Accra, Ghana, is home to over 100 000 people. Old Fadama has virtually no water or sanitation infrastructure, contributing to diminished quality of health and frequent cholera outbreaks when the nearby river floods. Our research introduces a model for cross-sector collaboration, supporting stakeholders who wanted to improve community health by installing latrines. Methods The focus of the research project is the process of cross-sector strategy development and the resulting theoretical model. Participatory action research (PAR) involves researchers and participants working together to define the problem and to formulate research questions and solutions. The project took place from Jan 1, 2015, to Nov 1, 2017. The participants were entirely local organisations, including stakeholders from city government, local non-governmental organisations, and the slum community. They resourced their own participation, made the strategy decisions, and selected the challenge to install latrines. The PAR process introduced the concept of cross-sector collaboration, educated the stakeholders about the existing evidence, and supported the stakeholders in forming a cross-sector collaboration. PAR was carried out in three phases. First, 12 key informant interviews were used to identify a location, barriers, and organisational strengths. Second, four focus groups developed a project strategy. Third, a community survey of 59 community members expanded the stakeholders and engaged the community in site selection and latrine management. 300 stakeholders participated over the course of the study as we continually updated and cross-checked our data through interviews and mini-focus groups to respond to the rapidly changing slum environment. Findings The stakeholders' first strategy, improving community health by installing latrines, resulted in city sanitation policy change. The strategy was adopted by local businesses, creating local sustainability and freeing the stakeholders to identify a new problem and develop a strategy to address it. Interpretation Diverse entities must collaborate effectively to impact and ultimately resolve complex health challenges. Our model utilizes Sustainable Development Goal (SDG) 17 (partnerships) in order to achieve SDG 3 (good health and wellbeing) and SDG 6 (clean water and sanitation). The research model is an innovative approach to cross-sector collaboration based on a theory-of-change design that is being pilot tested to develop new strategies in other slums in Accra. Funding Conrad N Hilton Foundation.