This article tackles a relatively under-studied aspect of the Christianisation of the Roman aristocracy. It considers the influence of Christian norms on a key stage in the elite male life course: service to the state. Drawing on the letters of Isidore of Pelusium, Augustine of Hippo and Theodoret of Cyrrhus to imperial officials, this article argues that a Christian rhetoric of office-holding had developed across the Mediterranean by the first half of the fifth century. It traces these authors’ varying expectations of how the religious identities of elite Christian men would shape their political agency. Their letters demonstrate the diffusion of Christian political ideas within the imperial state — and the terms on which Christian affiliations and traditional public careers were understood to be compatible — under the Theodosian dynasty.