Populist politicians are often associated with the successful use of social networking sites (SNS). However, it is still unclear whether the popularity of populist posts is driven by the nature of the messages, by the populist actors as the source, or by the interaction of both factors. By following a 2 × 2 experimental design ( N = 647) and by manipulating populist versus nonpopulist messages in a Facebook post and a typically populist versus mainstream politician as the source, this study contributes to the existing literature in two ways. First, it shows that both populist messages and populist actors foster the perception of a Facebook post as populist but that only populist messages are drivers of user reactions. Second, complementing content analyses on populism and user reactions, the study demonstrates that the effect of populist communication on user reactions is moderated by recipients’ populist attitudes. Users with strong populist attitudes share populist messages more often than they share nonpopulist messages.