Assistive Technology (AT) plays a crucial role in providing aid products, including prostheses to persons with disabilities. Tarsometatarsal (TMT) disarticulation, a type of partial foot amputation, is associated with complex gait disorders. However, there is limited research on the functional impact of TMT prostheses on gait. This study aims to develop and functionally validate a 3D-printed TMT prosthesis using finite element analysis and human motion laboratory studies. A 65-year-old patient with TMT amputation participated. Digital models of the amputated and healthy feet were obtained through 3D scanning. The prosthesis design was created using Fusion 360 software. Finite element analysis validated the prosthesis design. The prosthesis was manufactured using thermofusion printing with a biocompatible thermoplastic elastomer material. Functional validation included walking, running, and the Timed Up and Go test using motion analysis technologies. Finite element analysis demonstrated the structural integrity and safety of the TMT prosthesis during propulsion. The manufacturing process resulted in an adjustable and cost-effective prosthesis. Functional validation revealed improvements in gait quality, symmetry, and spatiotemporal parameters with the prosthesis. Vertical ground reaction forces during walking resembled the normal range, and running performance showed increased symmetry and propulsion velocity. The Timed Up and Go test showed that prostheses reduce time and improve efficiency. The development and functional validation of the 3D-printed TMT prosthesis offer a promising solution for individuals with TMT disarticulation. This approach addresses the need for assistive technologies in low-income countries with limited access to prostheses. Advanced technologies and a patient-centred approach contribute to improving mobility, gait patterns, and overall quality of life for individuals with partial foot amputations. Future research will focus on exploring additional parameters and developing new prostheses to further enhance gait improvements.