The article provides and empirically tests an analytical model that considers the relationship between the discretionary power of street‐level bureaucrats (SLBs) and the institutional and organisational structures at meso and macro levels. The proposal maintains a bottom‐up perspective in the analysis of discretionary practices; at the same time, it highlights the relevance of multilevel governance systems as institutional spaces in opening and constraining the room for manoeuvre of SLBs. The analytical model is tested to comparatively analyse the implementation of the Italian guaranteed minimum income (Reddito di Cittadinanza) in two different regional welfare systems. The analysis focused on the practices and perceptions of the “navigators”, a new professional group introduced to implement the same policy. The fieldwork pointed out different spaces for and forms of discretion, highlighting that different institutional arrangements affect discretion and the variability of practices; however individual and professional group factors coupled with similar external constraints nuanced this variability with the emergence of common ones. In this article, the analytical model allowed to consider in a comparative perspective how institutional factors, besides individual and professional ones, influence discretion.