As populists rise from periphery to power, the question of whether and how these actors threaten democratic institutions becomes ever more pressing. While previous research has focused primarily on the determinants of populists' electoral success and its consequences for voters as well as established parties, this article examines the impact of populist parties' government participation on the most fundamental of democratic institutions, the constitution. Drawing on a comprehensive dataset, covering information on constitutional changes and populist parties across 30 European democracies (1978-2019), I investigate how the entrance of these actors into power impacts the frequency and content of constitutional redrafting. I argue that populists in power not only commonly engage in projects of constitution-making and constitutional reform, but further pursue a specific agenda with these changes by increasing executive power and decreasing judicial independence. I test my argument using a series of fixed-effects and difference-in-differences models. The findings make an important contribution to the literature on populist parties, constitutional change and democratic backsliding.