In contexts of autocratisation and political polarisation, maintaining the legitimacy of policy expertise is cumbersome. Experts are clustered on two sides of the political divide: those not aligned with either side are excluded from regular policy processes, while those aligned to the regime are too close to the government to be seen as legitimate. This article analyses how policy-knowledge producers work towards achieving legitimacy for the knowledge they produce in such highly politicised contexts. It identifies three sets of legitimacy-building practices used to navigate the dominance of the political. First, knowledge producers increasingly embrace values-driven practices rather than insisting on neutrality and independence. Second, boundaries between political arenas and epistemic authority are tightened by the separation of individual and organisational identities. Third, the relevance of policy knowledge is reframed by diversifying audiences and outcomes to maintain usefulness. The practices identified are not specific to autocratising contexts, but they are exacerbated and become coerced responses to the hard constraints of an incrementally closing regime. Based on interview data with think tanks in Hungary’s polarised autocracy and highly politicised policy making, this research examines populist tendencies of questioning truth and neutrality of knowledge and expertise – all hallmarks of today’s turbulent policy environments. This makes it a valuable contribution to the broader literature on how think tanks negotiate legitimacy in contexts of de-democratisation.