This article analyzes the role of ideas, domestic actors, and international influences in migration policy change (MPCh) in Argentina, Brazil, and Chile. Building on 67 in-depth interviews with key actors in migration governance, public declarations of government representatives, and relevant legislation, we argue that the increased power of “securitist” actors within national bureaucracies shaped MPCh in all three countries. Between 2015 and 2019, these actors promoted a set of programmatic ideas and policy proposals that linked migration to security issues and distinguished between “good” and “bad” immigrants, emulating Global North countries. This set of ideas resulted in policy change at the country level, but at the same time, national-level policy change coexisted with continuity at the regional level. This article contributes to the literature on migration governance, first, by extending the geographical focus of migration policy studies, which frequently focus on party politics, coalitions, and public opinion, beyond the Global North. Second, we further current explanations of MPCh and policy contradictions by differentiating between continuity and change in programmatic ideas, policy proposals, and public philosophies. Third, we advance the regional migration policy literature by distinguishing between different groups of actors within national bureaucracies and enhancing understanding of these actors’ roles at both the national and international levels. Across its sections, this article shows that policy ideas—where and from whom they come—matter. By unpacking the different types of ideas that influence policy shifts and the actors who promote them, we can better understand apparent contradictions in migration policy.