Concrete experiences degradation in mechanical properties when exposed to high temperatures, leading to spalling, disintegration, and surface damage. Research shows a 26-40% reduction in structure strength under fire. While strengthening and restoring existing structures is a practical solution, a more sustainable approach is needed. This study evaluated the performance of sisal fiber mat retrofits for post-fire damaged beams and investigated natural fiber retrofits as a sustainable solution for fire-damaged structures, addressing challenges like elevated temperatures and moisture sensitivity to restore safety, stability, and functionality. The physical, chemical, and mechanical properties of the constituent materials used to fabricate the reinforced concrete beams and retrofitted material were characterized. The mechanical properties of 150×225×650 mm reinforced concrete beams exposed to 800 °C for 1 hour were assessed. The load-carrying capacity of the concrete beam was determined after it had been repaired with one or two layers of sisal fiber mat. The results indicated that the load-carrying capacity of concrete reinforced beams exposed to fire was reduced by 13.03%. However, the use of two layers of sisal fiber mat retrofits in the beams restored the load-carrying capacity by 33.86% and improved ductility by 43.56%. These findings demonstrate the feasibility of using sisal fiber mat retrofits to repair fire-damaged reinforced concrete beams, as the fiber mat enhances the load-carrying capacity by providing additional tensile strength to the structure.