Waste management has emerged as a critical challenge in multiple countries, where governance structures frequently exhibit insufficient robustness. Environmental non-governmental organizations (ENGOs), as pivotal stakeholders in this domain, must assume a more substantial role. However, their contributions have historically been perceived as limited. Whether and how ENGOs can play an important role deserves the attention of researchers. This paper investigates the evolving role of China's ENGOs through a longitudinal case study of nine organizations, examining their transition from adversarial to co-productive strategies, thereby fostering a tripartite collaboration system among government, enterprises, and residents. The findings reveal a three-phase evolution in organizational structure, issue focus, and tactical approaches, culminating in a three-cycle co-production framework for waste management. This study not only enriches co-production theory but also provides valuable insights into the critical role of ENGOs, offering practical guidance for sustainable waste governance.