The sustainability of solid waste management projects remains a major challenge in many developing countries despite substantial investments in infrastructure and technology. This study examined the effect of stakeholder participation on the sustainability of solid waste management projects in Uasin Gishu County, Kenya. The study was guided by Stakeholder Theory. The study adopted a descriptive research design. The target population consisted of 250 different individuals actively involved or affected by SWMPs in the county. A sample size of 152 respondents was achieved using the Yamane formula. Participants was sampled using stratified sampling. The information was collected using questionnaires, and a pilot study was carried out in Nakuru City to determine the validity and reliability of research instruments. The data was subsequently coded and placed into a computer where the Statistical Package for Social Sciences (SPSS Version 25) was used to analyze them. The data was analyzed using descriptive and inferential statistics. The descriptive statistics was based on frequencies, percentage, mean and standard deviation and inferential statistics were correlation and regression analysis. Analyzed data was presented in form of tables. The results revealed that stakeholder participation has a positive and significant effect on sustainability of Solid Waste Management Projects in Uasin Gishu County, Kenya (β1=0.207, p=0.004). The study concluded that Stakeholder participation is crucial for sustainability of Solid Waste Management (SWM) projects in Uasin Gishu County. It recommends that county governments institutionalize stakeholder participation frameworks that promote regular consultation, transparency, and community engagement in waste management initiatives. The study contributes to policy and practice by providing empirical evidence that stakeholder participation is a critical determinant of sustainability in public environmental projects and underscores the importance of inclusive governance for effective solid waste management in Kenya.