This paper aims to explore how an individual actor, acting as change agent, legitimizes the implementation of Integrated Reporting. A longitudinal and explanatory case study was realized by focusing on an Italian listed public utility, operating in the electricity sector, which has recently implemented the Integrated Report. Findings were analyzed through the lens of institutional entrepreneurship which explains how actors can achieve substantial changes. This paper unveils how the adoption of the Integrated Report can be achieved thorough the legitimizing activities carried out by a CSR manager, characterized by strong intrinsic engagement, who makes the best use of available resources and intense networking. Findings reveal that a substantial change in organizational structure, processes and thinking can be achieved over time through the perseverance of a change agent who strives to legitimize his credibility and projects within the organization by gaining support and collaboration from various organizational groups.