Abstract Although the scholarship on legislative behaviour widely agrees that electoral rules determine parliamentary activities, surprisingly little is known on the impact of gender quotas. We contribute to this research gap by developing an innovative interdisciplinary framework and by exploring it based on a unique dataset on varying gender quota designs throughout EU countries and parties running for the 7th term of the European Parliament (2009–2014). Based on the scholarship on gender diversity in management teams and the research on gendered processes in political parties, we argue that especially mandated gender quotas stimulate processes of social categorisation, intergroup biasing and competition due to a normative mis-fit between conceptions of gender equality and gender quotas, which in turn influences coordination and communication and hence, parliamentary activity more generally. Combining negative-binomial regression models and expert interviews, we indeed find that mandated gender quotas promote ‘individual’ parliamentary activities (e.g. speeches) and tend to impede ‘collaborative’ parliamentary activities (e.g. reports).