An alkali-activated precursor yields a stable, solid aluminosilicate material known as geopolymer. The properties and attributes of Geopolymer Concrete (GPC) vary greatly based on the type of raw material used. The current work used fly ash and ground granulated blast furnace slag (GGBFS) as raw materials to produce ambient-cured GPC. The two fine aggregates most frequently used in concrete are river sand and M sand. The over-exploitation of these natural resources will affect the environment’s equilibrium. To address the environmental concerns arising from the over-exploitation of natural fine aggregates like river sand and M-sand, copper slag was incorporated as a replacement in varying volume fractions (20%, 40%, and 60%) in M40 grade GPC. The findings reveal that copper slag significantly enhances the mechanical and durability properties of GPC. At an optimal replacement level of 40%, the compressive strength, split tensile strength, and flexural strength increased. Durability tests indicated that specimens exposed to H2SO4 and HCl exhibited minimal weight loss after 90 days. Furthermore, at 40% copper slag replacement, sorptivity and water absorption were 20% and 13.1% lower, respectively, compared to the standard mix. This study highlights the potential of copper slag to promote sustainable construction practices by reducing dependency on natural resources and managing industrial by-products effectively.