This study explores the evolution of the Green Grants program, run by Brazil’s Ministry of Environment, as a means for developing the concept of bureaucratic activism. When the Workers’ Party first took office in 2003, many social movement actors joined the government, especially in that agency. After 2007, however, most of these activists left the government. At the same time, the ministry substituted thousands of temporary employees for permanent civil servants. Surprisingly, this study finds that these public employees carried forward the environmentalist cause, even when this required contesting the priorities of superiors. Examining their attitudes and practices leads to a definition of activism as the proactive pursuit of opportunities to defend contentious causes. The case study helps to develop this concept and to demonstrate that workers inside bureaucracies can engage in activist behavior. It also explores the effects of bureaucratic activism on environmental policymaking in Brazil.