A core assumption in the impression management literature is that organizations voluntarily disclose information about their positive social and environmental activities, policies, and performance in order to improve or maintain their reputation as socially responsible actors and to garner stakeholder support. This assumption is at odds with an emerging and less well understood communication strategy of proactively disclosing socially irresponsible performance, a phenomenon which we call public confession. Combining a national survey of 525 corporate Black Lives Matter statements, a qualitative study of a business school’s Diversity, Equity, and Inclusion communications, and an experiment on labor and environmental issues, we investigate how audiences evaluate public confession. We examine whether, when, and why public confession mobilizes public support for a social issue and whether, when, and why it improves an organization’s reputation for being socially responsible. We find that public confession mobilizes public support for a social cause and improves an organization’s reputation for being socially responsible when the public believes that socially irresponsible business practices are pervasive. In this case, public confession does not violate expectations, but signals organizational authenticity. Consistent with this mechanism, the benefits of public confession are greater when firms confess something negative they have done (confession of commission), than when they confess something that they have failed to do (confession of omission). Our paper defines a boundary condition for studies of impression management, social movement framing, and signaling, explicates a novel non-market strategy in the context of rising corporate activism, and contributes to research on organizational reputation, impression management, and institutional theory.