Popular sovereignty is significant in a democracy as it underscores the principle that the authority of government derives from the consent of the governed. This concept ensures that political power is not concentrated in the hands of a few but rather reflects the will of the people. By empowering citizens to participate in decision-making through voting and civic engagement, popular sovereignty fosters legitimacy and accountability in governance. It reinforces the notion that governments must serve the interests of all citizens, ultimately enhancing democratic vitality.