Medical humanities scholarship has long emphasised the role of narrative in clinical practice, where it is valued for humanising medicine and revealing the subjective dimensions of illness. This focus has shaped the dominant view of the role of narrative in public health, where it is typically positioned as a means to render abstract data more ethically resonant, amplify marginalised voices, and support moral or political engagement. While this framing has enabled important forms of interdisciplinary collaboration, it also narrows how narrative is understood, construing it as a tool for communication rather than as a mode of explanation. This paper argues that such a view overlooks the role narrative reasoning already plays within population health science itself. Drawing on work in philosophy of science and population health, it shows that key explanatory practices—especially those concerned with temporally extended, socially embedded and structurally conditioned outcomes—require narrative forms of reasoning. Recognising narrative’s role in population health explanation repositions medical humanities from a communicative adjunct to an epistemic collaborator, capable of analysing the forms of reasoning on which population health science depends. In doing so, it expands the field’s methodological contributions and opens new possibilities for interdisciplinary research on structural inequality and health.