Mindfulness has shown a promising effect on reducing aggression in both clinical and non-clinical populations, possibly because mindfulness can improve emotion regulation. There is no theoretical model, however, that explains the specific mechanisms by which mindfulness might reduce aggression via better emotion regulation functioning. A comprehensive model that explains the mindfulness-aggression link is required to evaluate the effectiveness of mindfulness on reducing aggression. Thus, the present study examined the association between mindfulness and aggression with a focus on the mediating effect of different emotion regulation strategies. University and community samples of U.S. adults completed questionnaires on mindfulness, emotion regulation strategies, and aggression. Results indicate that mindfulness was associated with less use of maladaptive emotion regulation strategies (e.g., rumination, expressive suppression), which mediated the relationship between mindfulness and aggression. Mindfulness was not related to increased use of adaptive emotion regulation strategies (e.g., reflection, cognitive reappraisal). The nonjudging of experience facet of mindfulness predicted lower aggression through rumination and expressive suppression, such that highly nonjudging people were less likely to engage in rumination and expressive suppression and reported lower levels of aggression. In contrast, people high on observing facet reported more verbal aggression, anger, and hostility than those who are lower on this facet; these relations were mediated by the use of more rumination and expressive suppression.