<p>The increasing demand for low-carbon construction materials has increased interest in natural fibres as sustainable reinforcement in cementitious composites. However, ramie-based hybrid fibre systems combined with silica fume remain largely unexplored. This study investigates the synergistic behaviour of silica fume modified hybrid natural fibre reinforced cementitious composites incorporating ramie, coir, and sisal fibres. Hybrid systems were developed with a constant fibre content of 1%, with proportions ranging from 0.2:0.8, 0.4:0.6, 0.6:0.4, and 0.8:0.2, while 10% silica fume was used as a partial replacement of cement to enhance matrix densification. The results indicate that hybridisation significantly improves mechanical performance compared to single fibre systems. The coir–ramie (0.8:0.2) combination exhibited the best performance, with increases of 18.75% in compressive strength, 36.11% in split tensile strength, and 25.60% in flexural strength relative to control concrete. Microstructural analyses (SEM, EDS, XRD, FTIR, and TG–DTA) revealed a refined interfacial transition zone and enhanced formation of C–S–H gel, supported by a reduction in Ca/Si ratio from 1.98 to 1.46, indicating improved matrix densification and fibre–matrix bonding. Response surface methodology (RSM) and artificial neural network (ANN) models demonstrated strong predictive capability for optimising fibre proportions. Sustainability assessment showed that natural fibres significantly reduce embodied carbon compared to synthetic and metallic fibres. The findings highlight the potential of hybrid natural fibre systems for developing sustainable and high-performance cementitious composites.</p>