Why do some election boycotts turn violent while others do not? Existing research primarily studies electoral violence in competitive elections. In consequence, we lack knowledge on the causes of violence when the opposition boycotts the election and competition is limited. This study addresses this gap by combining insights on clientelism, nonviolent campaigns, and electoral violence, and argues that political clientelism incentivizes opposition violence and undermines conditions for nonviolent action. A cross-national analysis of all election boycotts in 1945–2022 demonstrates that boycotts in more clientelist settings are more likely to experience opposition and citizen-perpetrated violence. Moreover, a process-tracing analysis based on interviews and original event data on electoral protest and violence during the opposition’s boycott of Côte d’Ivoire’s 2020 presidential election elucidates the causal mechanisms at play. The study contributes new knowledge on the drivers of electoral violence during uncompetitive elections and about the relationship between political clientelism and electoral violence.