This study investigates the professionalization processes that accompany the integration of external mandates into mainstream organizations. In response to evolving societal pressures, organizations often create roles specifically tasked with developing practices that align with these external demands. Using the case of environmental, social, and governance (ESG) analysts in asset management companies, this longitudinal study examines the evolution of the ESG analysts’ occupational mandate through three distinct phases. Our findings reveal that ESG analysts’ mandates have developed along technical and normative dimensions, reflecting shifts in both required skills and professional ethos. This study contributes to the professionalization literature by illustrating how external mandates are reinterpreted and adapted within organizational settings.