This study tests whether social media disinformation contributes to domestic terrorism within countries. I theorize that disinformation disseminated by political actors online through social media heightens political polarization within countries and that this, in turn, produces an environment where domestic terrorism is more likely to occur. I test this theory using data from more than 150 countries for the period 2000–2017. I find that propagation of disinformation through social media drives domestic terrorism. Using mediation tests I also verify that disinformation disseminated through social media increases domestic terrorism by, among other processes, enhancing political polarization within society.