The sustainability of development projects is increasingly critical in addressing poverty and promoting inclusive growth; however, in arid and semi-arid areas like Kajiado County, many community-based initiatives fail due to poor project design, with up to 65% collapsing within three years despite substantial investment. This study examined how project design influences the sustainability of the Health and Livelihood Improvement (HELI) Project in Kajiado County. Anchored on Maslow’s Hierarchy of Needs Theory and supported by the Logical Framework Approach, Theory of Constraints, and ResourceBased View, the study adopted a descriptive research design targeting 1,000 stakeholders, from which 278 were sampled using simple random sampling in Olchoronyori and Oloirien villages. Data was collected using structured questionnaires and key informant interviews, with instruments showing strong validity (CVI = 0.81) and reliability (Cronbach’s Alpha = 0.89). Analysis using SPSS v26 applied both descriptive and inferential statistics, revealing that Project design significantly influenced sustainability. The study concluded that sustainability is best achieved through an integrated project design and recommended participatory planning, capacity building, and policy integration. Further research in other geographic and sectoral contexts was suggested to validate and expand these findings.