The unconventional nature of Holy See diplomats rests in the composite character of their ecclesiastical role as the Pope’s representatives and their legal diplomatic status and commencement to ordinary diplomatic practice. Holy See diplomacy is a form of conduct created by a set of mixed secular and religious standards in which agents are guided by practices. I locate this argument within a classical English School and a conventional understanding of practice, diplomacy, and agency while incorporating understandings of the diplomat as a stranger. The article situates a Holy See diplomat’s mode of agency as a hybrid one by nature, located at the intersections of political and religious modes of agency and substantial and relational conceptions of international politics. I probe this conceptual framework of hybrid agency by analysing episodes involving papal diplomats in turmoil-ridden historical episodes, and correspondence with informed agents.