What makes a bureaucracy effective? Conventional theories of bureaucratic effectiveness draw a sharp distinction between high-performing Weberian and low-performing patrimonial administrations, yet this dichotomy fails to explain China's development with a bureaucracy riddled with patrimonialism and corruption. I argue that instead of being merely a source of inefficiency, patrimonial institutions such as patron-client relations can help improve bureaucratic performance by resolving key principal-agent problems common within hierarchical organizations. Using an original city-level panel dataset between 2000 and 2011 and a new method that identifies patronage ties based on past promotions, I show that city leaders with informal ties to the incumbent provincial leader deliver significantly faster economic growth than those without, and that the performance premium is driven primarily by enhanced incentives of the connected agents. Analysis of an unexpected pollution-reduction campaign between 2007 and 2011 provides further evidence of the existence of patronage-based mobilization in policy areas other than economic management. These findings highlight the importance of informal institutions in bureaucratic management and authoritarian governance.