In the context of road subgrade stabilization, this research explores into the innovative application of geopolymer cement (GC) as chemical activator for enhancing the engineering properties of a blended soil composition prevalent in coastal Karnataka region, namely Lateritic Lithomarge, comprising lateritic soil and lithomargic (shedi) soil in various levels. The investigation draws inspiration from prior studies on lateritic and shedi soils in the region, recognizing their unique challenges and susceptibilities. Utilizing blended soil, the study explores the effectiveness of GC, synthesizing slag and fly ash as integral binder precursors. Geopolymerization, facilitated by an aqueous solution of sodium silicate-hydroxide mix, serves as the chemical activating agent. This stabilization process involves cementation and chemical alterations within the soil matrix induced by GC. Enhanced compaction properties, unconfined compressive strength (UCS), and California Bearing Ratio (CBR) values are meticulously examined and elucidated. By the trials, the optimal GC dosage was found to be 15–20% for the selected blended soil. Furthermore, the study extends its insights into pavement composition design (both flexible and rigid pavement), aligning with Indian standards, presenting a comparative analysis of the performance disparities between stabilized and unstabilized pavement subgrades. By focusing on the GC as a sustainable solution, the study contributes to the evolving landscape of sustainable pavement design in the realm of road infrastructure. The incorporation of blast furnace slag and fly ash in GC underscores its sustainable attributes, aligning with global efforts toward eco-friendly construction practices and resource optimization.