The problems of violence in Latin America are often reiterated, yet understanding how and why violence declines is far less common. While urban violence takes different forms and has a range of motivations, we suggest that strengthening political and social institutions are important in violence reduction processes. We examine this using a comparative analysis of two cities which have recently seen unusual and marked reductions in lethal violence: Bogotá in Colombia and Recife in Brazil. Drawing on primary data collection, the case studies suggest that novel leaders who take advantage of critical junctures can deliver unexpected improvements to public security; and improvements are linked with institutionalising progressive security policies, increasing accountability of political institutions, and social reforms encouraging civic values and commitments to non-violence. While findings are specific to these two cases, they may plausibly apply to a broader range of cities, such that commitments to improve public policy and political institutions can overcome structural risk factors that foster violence.