jats:titleAbstract</jats:title>jats:pWe describe a replicable process for coproducing a theory of ‘thriving’, or more broadly ‘wellbeing’, in partnership with stakeholders to inform an area of policy. Coproduction promotes effectiveness, practicality, and legitimacy of wellbeing policies by combining insights from people with lived experience of that policy, the practitioners who implement it, and technical experts with relevant area specific knowledge. We illustrate our methodology using a case study of a coproduction exercise between wellbeing researchers and practitioners and users of Turn2us, a UK-based anti-poverty charity. We report both the process developed for this collaboration and the bespoke theory and measures of thriving in financial hardship that emerged from it. We emphasise the interplay between different types of inputs: quantitative and qualitative data, academic theories of wellbeing and lived experience, and formal and informal insights. Our experience demonstrates the value of contextualising wellbeing for practical contexts, serving as an important complement to top-down approaches relying on standardised theories and metrics.</jats:p>