<p>This study systematically investigates the mechanical performance, durability characteristics, and impact resistance of one-part alkali-activated mortars produced from ground granulated blast furnace slag and fly ash, reinforced with micro steel fibers, activated using dry sodium silicate and sodium hydroxide powders. The primary objective is to enhance the mechanical and durability properties of these sustainable mortars for practical structural and impact-resistant applications. Fourteen different mix compositions were prepared, categorized into plain and fiber-reinforced groups, with reinforced mixtures containing 0.25% micro steel fibers by volume. Mechanical properties assessed include compressive strength, splitting tensile strength, and flexural strength. Durability was evaluated through freeze–thaw cycling, capillary absorption, and water absorption tests. Impact resistance was assessed under both static (repeated drop-weight test) and dynamic (drop hammer test) loading conditions. Results demonstrate significant performance improvements in fiber-reinforced mixtures, with increases of approximately 25% in compressive strength, 47% in splitting tensile strength, and 51% in flexural strength compared to plain mixtures. Fibers notably enhanced energy absorption capacity, showing an approximately 85% increase under static loading and 75% under dynamic loading, highlighting their effectiveness in energy dissipation. Predictive regression models developed for flexural strength, splitting tensile strength, impact energy, and ultrasonic pulse velocity showed strong correlation with experimental data, providing practical tools for design and quality control. Overall, this study underscores the significant potential of fiber-reinforced one-part alkali-activated mortars as sustainable, high-performance alternatives for structural and impact-resistant construction applications.</p>