A long tradition of studies in political science has unveiled the effects of electoral institutions on party systems and parliamentary representation. Yet their effects on campaign activities remain overlooked. Research in this tradition still lacks a strong comparative element able to explore the nuanced role of electoral institutions in shaping individual-level campaigns during first-order parliamentary elections. This study uses data from a variety of national candidate studies to address this lacuna, and shows that the structure of electoral institutions affects the electoral mobilization efforts put in place by candidates. Candidate-centred electoral systems incentivize more intense and complex mobilization efforts, and shift the campaign focus towards individuals rather than parties. By directly addressing the effects of electoral institutions on campaign behaviour, this study contributes to the wider debate on their role in promoting political engagement and mobilization. These results indicate that electoral institutions affect political competition much more than previously thought.