Citizen participation makes an increasingly important effect on co-creating public value required by the sustainable governance of societies. The offline action participation authentically brings government policies into force but could not be automatically quantified, while online opinion participation could implement diverse incentives by recording participation process but make limited contribution to the governance of societies. The isolation deters them from complementing with each other. Therefore, according to the social exchange theory we propose an O2O (Offline-to-online) citizen participation ecosystem for the sustainable governance of societies. It includes three key participants (citizen, government organization, and O2O platform manager) and five components (motivations, contextualized governance policies and strategies, offline action participation, online rewards collection, and retainment & recommendation). The ecosystem is validated and improved by a case study on the O2O green commuting governance in China. This study enhances the effective combination of online and offline citizen participation through a closed-loop process.