This chapter argues that the Age of Revolution and, more specifically, the Jacobin turn in the French Revolution, is a key moment in the genealogy of modern populism. It does so by exploring Filippo Mazzei’s views of the American and French revolutions. Mazzei was a merchant and writer from the Grand Duchy of Tuscany. He participated in the American Revolution and was in Paris when the French Revolution broke out. Historians often view him as a human bridge between the two revolutions of the ‘age’ and no one would doubt his support for popular sovereignty. Yet, he did not believe that popular sovereignty could and should be pursued at any cost. In particular, he criticised the turn that the French Revolution took in the early 1790s under Jacobin leadership. Mazzei saw the Jacobins as ‘new demagogues’ who aimed to establish ‘universal disorder’. He also believed that the development of popular sovereignty should be guided by existing institutions and criticised the idea that those institutions could be demolished to fulfil the will of ‘the people’. If populism is a style of political conduct that privileges the actions of charismatic leaders while discrediting or bypassing traditional representative institutions and justifies itself by appealing to the will of ‘the people’, we can argue that Mazzei rejected the ‘populist’ turn taken by the French Revolution. The chapter concludes that the Age of Revolution was as much a cradle of popular sovereignty as it was one of (proto-)populism.