This study explores an innovative solution through the development of smart, multifunctional mortars made from natural hydraulic lime (NHL) reinforced with carbon microfibers (CMFs). The research thoroughly evaluated the mechanical properties, electrical characteristics, and piezoresistive behavior of NHL mortars containing 0.05%, 0.10%, and 0.20% CMF by binder weight. The results identified 0.10% CMF as the optimal dosage, resulting in enhanced electrical conductivity, high piezoresistive sensitivity, and stable sensing linearity under compressive loads while maintaining compatibility with historic structures. Notably, the incorporation of sand aggregates significantly improved fiber dispersion and mechanical performance compared to paste formulations, addressing common challenges such as strength reduction and signal variability. These findings demonstrate the strong potential of CMF-modified NHL mortars as dual-purpose materials that combine structural functionality with self-sensing capabilities, providing a promising solution for non-invasive monitoring and smart interventions in architectural heritage conservation and sustainable infrastructure systems. This technology effectively bridges the gap between modern sensing needs and historic preservation requirements, ensuring both technical performance and aesthetic compatibility.