To enact social movement goals and create social change, external activists often wish to bring about change within target organizations. Yet, research demonstrates that organizational change is difficult. Even if there are internal advocates who are motivated to enact the desired social change, these internal change agents often face barriers to mobilizing support. In this paper, we ask: How do external activists enable internal change agents in target organizations to implement desired social changes? Using a 15-month ethnography of an organization attempting to spread caregiver support benefits by influencing target organizations through insider allies, this paper develops theory about social movements and organizational change. Specifically, we identify practices through which external activists help internal agents overcome positional barriers to implementing change. Our findings demonstrate how the external activists strategically developed catalyzing resources, which we define as resources deployed by an external actor to facilitate internal agents’ implementation of organizational change. Further, the external activists equipped internal change agents to mobilize these catalyzing resources to overcome their limited power and authority in implementing change – including selling the change to executives and employees, and measuring impact to sustain devoted resources. We thus illustrate how the barriers faced by internal agents created opportunities for external activists to help those agents and in doing so, strategically influence change implementation.