This paper examines the medical identity propagated by the Belgian Saint Luc Society. By scrutinizing the society’s journal Saint-Luc Médical, it shows how the society forged and spread a model for being a Catholic physician, a ‘physician-apostle for Christ’. Our analysis reveals that lay apostolate, a central element of the interwar Catholic Action movement, was at the heart of this new professional identity. It imbued an older vocational discourse with decidedly Catholic views of doctors’ social responsibilities. The paper first places the society’s foundation within the broader history of Belgian medical sociability. Secondly, it looks at how the society functioned as a laboratory for unifying Catholicism and Medicine. Here physicians and theological advisors discussed and created Catholic infused medical ideas. Lastly, the article considers how society’s journal transmitted an image of the ideal physician to its readership. Catholic doctors reading Saint-Luc Médical were expected to follow strict deontological advice and theological guidelines. This way, the journal cultivated a sense of moral superiority towards non-religious colleagues.