The achievement of global sustainability and climate objectives rests on their incorporation into policy-making at the level of nation-states. Against this background, governments around the world have created various specialized sustainability institutions—councils, committees, ombudspersons, among others—in order to promote these agendas and their implementation. However, sustainability institutions have remained undertheorized and their impact on policy-making is empirically unclear. In this paper, we develop a conceptual framework for sustainability institutions and systematically explore their potential impact on more sustainable policy-making. We define sustainability institutions as public, trans-departmental and permanent national bodies with an integrated understanding of sustainability that considers socio-ecological well-being, global contexts and a future-orientation. Drawing on literature on sustainability and long-term governance as well as on illustrative case examples, we propose conducive conditions and pathways through which sustainability institutions may influence policy-making. As conducive, we assume sustainability institutions' embodiment of sustainability governance principles as well as their authority, a strong legal basis, resources, and autonomy. Further, we outline how sustainability institutions can influence policy-making based on their roles in the public policy process. We conclude that the increasing prevalence of national sustainability institutions indicates an ongoing shift from the environmental state toward a more comprehensive sustainability state. However, sustainability institutions can only be one building block of the sustainability state out of many, and their potential to reorient political decision-making effectively toward the socio-ecological transformation hinges upon individual design features such as their mandate, resources and authority, as well as on the specific governance context.