Amid extensive research on the direct effects of shareholder activist demands on target firms, recent calls have been made to understand the broader system in which activism unfolds, including the actors that facilitate or hinder activists’ efforts. In this study, we develop a theoretical framework that positions the outcomes of shareholder activism as contingent on the actions of other third-party stakeholders. The fulcrum of our theory is that activist demands will more effectively motivate organizational change when other stakeholders reinforce the issues raised by shareholder activists. Situated in the context of shareholder proposals, we theorize and find that the potential for proposal-based activism to enact organizational change hinges on the scrutiny of proposed issues raised by the media and regulators, which, respectively, bring coverage and credibility to the issues at hand. This study steps beyond the activist-firm dyad to provide new insights into the role that non-shareholding stakeholders play in shareholder activism, and raises new questions about stakeholder governance.