Effective project implementation remains a persistent challenge in Kenya’s marginalized counties, where limited institutional capacity and weak stakeholder engagement often lead to project delays, cost overruns, and incomplete outcomes. This study examined the effect of technical capacity and stakeholder involvement on project implementation in Garissa County, one of Kenya’s least developed regions. The research was guided by the Resource-Based View (RBV) and Stakeholder Theories, which emphasize internal capabilities and participatory governance as key enablers of project success. A descriptive research design was adopted, targeting 250 project stakeholders drawn from various county departments. Using Yamane’s formula, a sample size of 154 respondents was selected through stratified random sampling. Primary data were collected using structured questionnaires, and reliability was confirmed through Cronbach’s Alpha coefficients exceeding 0.80. Data were analysed using SPSS Version 28, applying both descriptive and inferential statistics, including correlation and multiple regression analysis. The results revealed that both technical capacity (β = 0.247, p < 0.01) and stakeholder involvement (β = 0.209, p = 0.003) had a positive and statistically significant effect on project implementation in Garissa County. The overall model explained 64.1% (R² = 0.641) of the variation in project implementation, confirming the strong predictive power of the selected variables. The study concluded that enhancing technical competencies, providing adequate tools and systems, and promoting participatory stakeholder engagement are critical to improving project efficiency and sustainability in marginalized regions. It recommends that county governments institutionalize continuous capacity-building programs, strengthen stakeholder consultation mechanisms, and integrate participatory monitoring and evaluation frameworks. These measures would enhance accountability, foster ownership, and improve the timely completion and quality of public projects in Kenya’s devolved system.