The excessive consumption of natural sand can result in environmental issues such as erosion, depletion, and groundwater disturbances. This study aims to investigate the possible utilization of Omani marble waste as an alternative to natural sand in mortar, thus contributing to the ongoing revolution in waste management and sustainable construction practices. The mortar mixtures were designed at a constant water-to-cement (w/c) ratio of 0.5, and the weight percentage (wt.%) replacement of the wadi sand (WS) by the marble waste (MWS) ranged from 0% to 100% in increments of 20%. Characterization of the natural materials was conducted and the mechanical properties of cement mortars were determined after 28 days of water curing. This assessment included measuring flowability, fresh and hardened density, strength property, porosity, ultrasonic pulse velocity and examining microstructure characteristics. The results from the experimental testing program show that the mixture with 60–80% MWS replacement can be considered the optimal mixture, with higher compressive strength than the 0MWS blend. The research findings indicate that incorporating marble waste as a replacement for sand contributes to an improved mechanical performance of cement mortar.