The need for new private houses and large infrastructure is increasing all over the world. Cement is one of the construction materials available and its manufacturing is a very energy-consuming and greenhouse gas (GHG) emitter. Due to high cement demand, its cost is rising as well. This study aims to investigate the partial replacement of cement with granite and marble waste powder (GMWP) in cement mortar production. There were 10 mixes for pilot study with varying percentages of GMWP made before the actual mix to determine combination percentages of marble and granite waste powder then substantial experiments were carried out by partially replacing Portland cement with GMWP at 0%, 5%, 10%, 15%, 20%, 25%, and 30% by weight of cement as per ASTM C 109. The study investigated the chemical, mechanical (compressive strength, and ultrasonic pulse velocity(UPV)), durability (sulfate resistance and absorption), and microstructural properties fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray florescence (XRF), and scanning electron microscopy (SEM) of concrete when partially replaced by GMWP. Based on BET results marble and granite waste are very fine materials. At 28 days of curing, compressive strength had improved by 18% at 10% replacement, and uniformity had increased. Furthermore, the samples showed a reduction in water absorption capacity as the replacement percentage increased up to 15% replacement. Morphological structures of samples were improved when replacement increased. The loss of mass due to increasing temperature is increased with replacement percentage. Keywords: Granite Powder, Marble Powder, Fresh Mortar Properties, Mechanical Properties, Microstructure, Durability