The use of research evidence to change clinical practice remains a significant challenge. Quality improvement (QI) offers a methodological approach to support this ‘knowledge to practice’ process. However, most research on QI focuses on the use of knowledge and not its creation to improve practice. This research aimed to address this gap through an exploration of the social process of co-creating knowledge within a QI project. The case study aimed to improve the physical health of people with serious mental illness through the introduction of a physical health ‘pathway’. The QI project used participatory approaches to introduce new evidence-based clinical practices, initially on a single ward, and then scaled-up across five additional wards within an acute mental health unit in the National Health Service (NHS) in England. This four-year study used ethnographically-informed qualitative participatory approaches where the researcher was part of the QI project. Data were generated through participant observations, interviews and documentary analysis. The analysis included generating a narrative of the project, and the use of Knowledge Mobilisation and Implementation Science frameworks. This research offers a window on the social construction of a QI project. Improvement is a socio-technical process that relies on social practices to generate the work required to support the ‘knowledge to practice’ process. QI methods draw on the tacit knowledge and experiences of stakeholders which is codified in outputs from workshops, which in turn can be used in the co-design of interventions. This co-constitutive process of simultaneous knowledge ‘use’ and ‘creation’ contributes to the co-creation of collective understandings and meanings, which compose the social practices of QI. However, issues of responsibility and accountability pose a significant challenge, and a careful balance needs to be found between the use of the data for managing performance and supporting staff to reflect on their practice.