The moral entrepreneur is a social actor capable of turning social situations, perceived by themself as harming, into public problems. In line with Howard Becker's work, the criminological literature has looked at the processes of problem construction by moral entrepreneurs and their consequences. It explains how certain social situations are turned into public problems and how they are dealt with in the public arena. However, to achieve their self-attributed mission, moral entrepreneurs need to be, above all, feel legitimate to do so. This paper focuses on the legitimation devices put forth by moral entrepreneurs through the specific case study of Geneva’s philanthropy. Philanthropists take over various social harms and, in parallel, develop a narrative presenting themselves as legitimate to do so. This research, using a qualitative methodology (observation, interview, documentary analysis), unveils two main devices of legitimation: (1) The Fictional Pact, a narrative that functions as a self-legitimation tool on the moral level, and (2) the public legitimation, making a solid and supported claim that society needs philanthropy. More broadly, this study helps to understand better how private moral entrepreneurs justify their participation in society’s governance by bringing together two traditionally separate pieces of literature on legitimation.