In recent years, there has been an increased academic interest revolving the beneficial or pernicious effects of ideological polarization and (uncivil) political discussion over democracy. For instance, citizens’ ideological predispositions and higher levels of political discussion have been linked with a more active and vibrant political life. In fact, ideological polarization and uncivil discussion foster institutionalized political engagement. However, less explored in the literature remains whether such polarization and uncivil discussions may be related to unlawful political behavior such as illegal political protest. This study contends that one of the main drivers of illegal protest behavior lies on online uncivil political discussion, specifically through the normalization and activation of further incivility. We test this through a 2 wave panel data drawn from a diverse US sample and cross-sectional, lagged and autoregressive regression models. Mediation analysis was also conducted to test whether uncivil online discussion mediate the relationship between frequency of online political discussion and illegal protest engagement. Overall, we find that it is particularly online uncivil discussion what drives illegal protest, while ideological polarization and other forms of discussion online and offline seem to have no effect on unlawful protest over time.