Argentina is highly advanced in terms of LGBT rights whereas Chile has been slower to adopt pro-LGBT legislation. Yet, Chile passed an anti-discrimination law that includes LGBT protections while attempts to include them in Argentina were unsuccessful. This thesis asks why anti-discrimination legislation that includes sexual orientation and gender identity was not passed in Argentina but was successful in Chile. The study draws on the literature on social movements and moral policy to argue that it is the result of effective social movement mobilization that the legislation was successful in Chile but not Argentina. With data gathered from extensive fieldwork in both countries, I demonstrate that due to the weak mobilization in favour of anti-discrimination reform in Argentina the legislation has not been successful. In Chile, LGBT activists mobilized effectively in favour of the legislation which was crucial to the bill’s success. The thesis demonstrates the crucial role of social movements in the moral policymaking process.