The Kenya Agricultural Marketing Strategy (AMS) 2023-2032 highlights on leveraging digital technologies to enhance market access for smallholder farmers by integrating mobile applications and e-commerce platforms into the agricultural landscape. Yet, implementation of these technologies among smallholder farmers in Sub-Saharan Africa (SSA) remains a challenge. This paper analyzes the role of stakeholder involvement in the development process and implementation of agri e-commerce platforms in Kenya. A participatory action research (PAR) design was adopted, integrating Design Thinking, Lean Startup, and Agile methodologies within the Agricultural Innovation Systems (AIS) framework. Data were collected through baseline and endline surveys bearing in mind the platform analytics through user interaction with the agri e-commerce platform. Results of the study indicate that participatory co-design significantly improved platform outcomes with users increasing by 88.9% at exit / endline survey. Average transaction time for farmers decreased by more than half while user satisfaction scores improved by 37.5%. Additionally, stakeholder participation levels increased by 46%, confirming that inclusive engagement and iterative feedback loops enhanced usability, adoption, and implementation success. Statistical t-tests further revealed that users with higher digital literacy achieved significantly greater implementation success (p < 0.05). This study was however limited to one county context and a single digital platform namely warumarket presenting difficulty in generalization of results to other regions. The findings underscore the value of participatory innovation frameworks for sustainable agri e-commerce adoption in developing regions.