A mega-event is an open socioeconomic system characterized by massive budget demands and multiple types of subprojects and their complex interrelationships. Although a mega-event is an opportunity for a country to show its international reputation, management capacity, and societal strength, it demands a long preparation time; an enormous amount of investment; and massive resource mobilization, with far-reaching effects on both the economic and social development of a country. Mega-event projects (MEPs) face remarkable challenges in terms of overrun costs, delayed schedules, and political issues, indicating that the research on such mega-events is still insufficient and that there is a lack of effective theories to support the management and governance of MEPs. Existing studies have also ignored the dynamic evolution and adaptation of governance in a changing environment, particularly in relation to the success of MEPs. To fill this research gap, this study aims to examine the dynamic governance of MEPs on the basis of a new theory—evolutionary governance theory (EGT)—which combines institutional economics, systems theory, and project governance. The study was conducted in three main steps: (1) studying the case of the evolutionary governance of the World Expo 2010 in China during its life cycle stage, including planning, construction, operation, and post-event development; (2) discussing the impact of the hierarchical and cross-functional governance structure of the Expo; and (3) summarizing the theories and best practices of dynamic governance mechanisms for MEPs. The result of the study can deepen understanding of the multi-level governance of mega-events during the life cycle process and can also support the evolution of governance transition over the different stages.