The COVID-19 pandemic has constrained the ability of states across the world to govern and control their territories. As the state reduces its activities, space opens up for violent nonstate actors working for and against the state to fill the vacuum. Highlighting this trend, the present study evaluates the effects of COVID-19 and pandemics more broadly on attacks by nonstate actors. Our theory emphasizes the incentives of both rebels and pro-government nonstate actors (PGNs) to increase their attack frequency as disease spreads and the state retracts its governance activities to preserve resources needed elsewhere. In the first case, we highlight how the pandemic allows rebels to reduce asymmetries of power with respect to the military and establish themselves as a viable government alternative. In the second case, PGNs, which provide an alternative to militaries, are deployed to these contested spaces to thwart or preempt rebellion during the pandemic. Employing daily level data on the annual change in armed conflict and COVID-19 cases across 127 countries between 1 January 2020 and 15 June 2020, we test both claims using an econometric identification strategy. We do not find clear evidence that COVID-19 led to a higher frequency of rebel attacks, suggesting that these groups prefer to bolster their standing using nonviolent means, or avoid fighting and preserve their resources. In contrast, we find that the frequency of PGN attacks has increased with COVID-19 prevalence compared with last year. Case studies of insurgent and PGN activity in Afghanistan and Nigeria lend additional support to these results, illustrating some underlying mechanisms. Our findings explore overlooked challenges that pandemics and other disasters pose to conflict mitigation and the role PGNs play in these contexts.