Natural fibres have captured the attention of researchers and industries alike, thanks to their renewability, widespread availability, biodegradability, and cost-effectiveness. However, despite these inherent advantages, natural fibre reinforced polymer composites encounter significant hurdles that hinder their utilization in semi-structural and non-structural applications, primarily due to their susceptibility to moisture absorption. In this study, we delve into the potential of Mokolwane fibre, an innovative indigenous fibre sourced from Botswana, as a reinforcement for polymers. The fibre undergoes comprehensive characterization, including tests for fibre diameter, moisture absorption, thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM) analysis. Subsequently, composite specimens are synthesized using Mokolwane fibre and Polyester resin, with variations in fibre loading and alkali treatment concentration to determine optimal conditions. Moisture absorption assessments reveal that higher fibre loading increases water uptake by the composites, while alkali treatments effectively reduce this absorption. Mechanical property evaluations demonstrate that composites fabricated with 50 wt.% fibre loading and 4% NaOH fibre treatment exhibit optimal performance, with tensile strength, flexural strength, and impact energy reaching 76.5 MPa, 124 MPa, and 3.83 J, respectively. The enhancements attributed to alkali treatment are substantiated by SEM and FTIR results, indicating improved fibre-matrix interfacial adhesion resulting from the removal of hydrophilic amorphous surface components. However, excessive alkali concentration proves detrimental to mechanical properties, as it damages the fibre surface. Furthermore, inadequate fibre loading leads to inadequate stress transfer, while excessive loading results in cracks, voids, and fibre agglomerations. Based on the study findings, the Mokolwane fibre and composite demonstrate suitability for integration into diverse applications spanning automotive, construction, and furniture industries. This research not only contributes to achieving the United Nations' Sustainable Development Goals but also underscores the utilization of readily available, indigenous natural resources in industrial applications, thereby promoting sustainability and resource efficiency.