This article explores stakeholders’ perceptions of the challenges for developing a One Health agenda to tackle antimicrobial resistance (AMR) in Brazil, including the development and implementation of the Brazilian National Action Plan (BR-NAP). The data originate from 27 interviews conducted with human, environmental, and animal health stakeholders, including academics, managers, and policymakers involved in developing the BR-NAP. Through thematic analysis, we identified three interconnected themes: governance, the health system, and technical and scientific challenges. The findings draw particular attention to failures in the agenda-setting process, revealed by interviewees strongly emphasising that AMR is not considered a policy priority in Brazil. The lack of political will and awareness of the clinical, social, and economic impacts of AMR are considered the main impediments to the agenda’s progress. The joint work across disciplines and ministries must be reinforced through policymaker engagement and better environmental sector integration. The agenda must include sustainable governance structures less affected by political winds. Policies should be designed jointly with state and local governments to create strategies to engage communities and improve their translation into effective implementation.