Can deliberative mini‐publics contribute to deepening the democratic dimensions of electoral democracies? The question is framed in this article using a problem‐based approach to democratic theory–to count as democratic, political systems must accomplish three basic functions related to inclusion, communication and deliberation, and decision making. This approach is elaborated with an analysis of a real‐world case: a deliberative mini‐public with a citizens’ assembly design, focused on urban planning convened in Vancouver, Canada. This example was chosen because the context was one in which the city's legacy institutions of representative democracy had significant democratic deficits in all three areas, and the mini‐public was a direct response to these deficits. It was found that Vancouver's deliberative mini‐public helped policy makers, activists and affected residents move a stalemated planning process forward, and did do so in ways that improved the democratic performance of the political system. Depending on when and how they are sequenced into democratic processes, deliberative mini‐publics can supplement existing legacy institutions and practices to deepen their democratic performance.