For the era of the Third Republic, the trajectory of the path of senior official and great architect of French administrative law Jean Romieu (1858-1953) stands out, both for how long it lasted and for how he dedicated himself in particular to the works of the administrative claims department of the Conseil d’État. Based on a study of the archives of this jurisdiction under the Third Republic, the article thoroughly explains why this character was simultaneously isolated compared with other members and central for the institution. Insofar as the socio-biographical interest in the figure of Jean Romieu takes place in the broader context of a prosopographical enquiry on the exponents of the idea of public service between 1870 and 1940, the demonstration does not solely point out this jurist’s singularity: it also throws into relief what the latter accounts for regarding the transformations of the institution Romieu is part of, and how, in litigation affairs, it uses the singularities that come across to create, in a casuistic fashion, a “new” theory on public service. In line with Foucault’s perspective, administrative law is analysed as science of government and public service as an expression of pastoral power.