Argentina’s 2004 Migration Law spearheaded rights-based immigration policy reforms across Latin America. To deconstruct the policy process that enabled the passing of this ‘revolutionary’ law, we apply a mixed qualitative approach, based on secondary literature, and the analysis of 80 semi-structured interviews with key stakeholders. We argue that both structural and contingent regime dynamics shaped a window of opportunity for the reform to take place. We further show how key actors amongst civil society organisations, the executive and the legislative branches formed multi-sectoral coalitions and strategic alliances to turn this policy window into a critical juncture of lasting policy change. Ultimately, legislative reform was successful because it was framed as a human right, and not as an immigration issue. The paper contributes to scholarship on immigration policy determinants, ideational strategic alliances, policy windows and critical junctures.