Independent offices for future generations (OFGs) are rare amongst institutional designs that aim to ameliorate short termism in democracies. Drawing on the experience of OFGs in Israel, Hungary and Wales, the paper argues that such institutions face at least three challenges to their legitimacy. First, the capacity of an unelected agency to constrain government and law-making. Second, the ability of a single office to adequately represent the plurality of interests within and across future generations. Third, their political fragility and vulnerability. The article develops the counterintuitive argument that OFGs can enhance their democratic legitimacy through embedding systematic public participation in their activities, in particular through the institutionalization of deliberative mini-publics.