Massive volumes of overburden (OB) dump materials are produced by the coal industry during the mining of coal to meet the nation’s energy needs. Similarly, the steel industry produces by-products called basic oxygen furnace (BOF) slag and blast furnace slag (BFS). Disposal of these industrial wastes not only consumes valuable land but also puts the environment at serious risk. This study aims to utilize these wastes to create suitable and sustainable subbase/base course materials for flexible pavement systems in compliance with IRC 37-2018. To reduce the huge carbon footprint associated with Portland cement, geo-polymeric stabilization was done using alkali-activated BFS. For the alkali activation, liquid NaOH and Na2SiO3 mixture was used. Results show that a blend consisting of 40% OB dump, 40% BOF slag, and 20% BFS with 4 M NaOH and 1 M Na2SiO3 as activator yields the highest 7-day unconfined compressive strength (UCS) value of 5.23 MPa, satisfying the IRC 37-2018 specifications and considered as the optimum combination. A 12-cycle wet–dry durability test was also performed on the optimum mixture, and a mass loss of about 6.09% was found, which is well below the 14% allowable limit. To determine the impact of moisture fluctuation on strength, the retained UC strength after 12 cycles was also assessed. It was found that the strength loss was very less. This indicates the excellent long-term durability of the stabilized waste material in adverse weather conditions. A 40.36% cost reduction has been found by applying these waste materials with geo-polymeric stabilization in pavements layers. In summary, the integration of industrial waste materials into subbase/base layers helps in efficient waste management and conservation of natural aggregates and cost-effectiveness in the construction process. Moreover, the use of alkali activation significantly reduces the carbon footprint, thus promoting environmental sustainability.