Deliberative minipublics are popular tools to address the current crisis in democracy. However, it remains ambiguous to what degree these small-scale forums matter for mass democracy. In this study, we ask the question to what extent minipublics have “spillover effects” on lay citizens—that is, long-term effects on participating citizens and effects on non-participating citizens. We answer this question by means of a systematic review of the empirical research on minipublics’ spillover effects published before 2019. We identify 60 eligible studies published between 1999 and 2018 and provide a synthesis of the empirical results. We show that the evidence for most spillover effects remains tentative because the relevant body of empirical evidence is still small. Based on the review, we discuss the implications for democratic theory and outline several trajectories for future research.