The study investigates the competence of geopolymer and cement-stabilized expansive soil as sustainable road materials. The expansive soil was treated with different proportions of slag-based geopolymer (5, 10, and 20%) and Portland cement (4, 12, and 15%) by dry weight of soil. The plasticity behavior of expansive soil was reduced, and an improvement in the dry density and strength was observed with the addition of stabilizers. A compressive strength of 5.1 MPa is achieved with 20% geopolymer, whereas 15% cement develops a strength of 4.25 MPa at 28 days of curing. The efficacy of stabilized soil as road base-course material was assessed using a mathematical model of a two-layer flexible pavement system, and deformations were calculated under a standard axial dual-wheel load. The results showed that the geopolymer stabilized base course material has lower deformation than cement-stabilized and conventional granular base course materials. Further, environmental impact analysis was carried out using E-emission and E-energy as crucial parameters. This analysis indicated an eco-friendly behavior of geopolymer stabilization with 53.98% lower E-emission (0.0046 kg-CO2) and 12.46% lower E-energy (0.0521 MJ) per unit strength gain compared to cement stabilization.