We examine the eﬀect of group size of minorities on their representation in national government under majoritarian (MR) and proportional (PR) electoral systems. We ﬁrst establish a robust empirical regularity using an ethnicity-country level panel data comprising 438 ethno-country minority groups across 102 democracies spanning the period 1946–2013. We show that a minority group’s population share has no relation with its absolute representation in the national executive under PR but has an inverted-U shaped relation under MR. The pattern is stable over time and robust to alternate speciﬁcations. The developmental outcomes for a group proxied using stable nightlight emissions in a group’s settlement area follow the same pattern. We reproduce the main results by two separate identiﬁcation strategies—(i) instrumenting colony’s voting system by that of the primary colonial ruler and, (ii) comparing the same ethnicity across countries within a continent. We argue that existing theoretical framework with a two group set up is not able to explain this pattern. Our proposed model incorporates the spatial distribution of multiple minority groups in a probabilistic voting model and justiﬁes these patterns as equilibrium behavior. The data further validate a critical assumption of the model and its additional comparative static results. Our work highlights that electoral systems can have importanteﬀectsonpowerinequalityacrossminorities, andconsequently, theirwell-being.