Economic theory suggests that leaders may play key roles in enabling social movements to overcome collective action problems through a variety of distinct mechanisms. Empirical tests of these theories outside the lab are scarce due to both measurement and identification challenges. We conduct multiple field experiments to test theories of leadership in the context of Myanmar's burgeoning labor union movement. We collaborate with a confederation of labor unions as it mobilizes garment workers in the run-up to a national minimum wage negotiation. We present three sets of results. First, we document that union leaders differ from union members and non-members along several traits that psychologists and organizational sociologists have associated with ability to influence collective outcomes. Second, we randomly embed leaders in group discussions on workers' preferred and expected minimum wage levels. A leader's presence in the group improves group engagement and increases workers' consensus around the unions' preferred minimum wage levels. Third, we conduct a mobilization experiment in which workers are invited to participate in an unannounced activity that features strategic complementarity in turnout. Leaders influence participation through both coordination and social pressure mechanisms rather than by simply motivating workers.