In recent years, the use of industrial and municipal waste materials in stabilizing problematic soils—particularly clayey roadbeds—has emerged as a sustainable and environmentally friendly strategy in geotechnical engineering. Clay soils exhibit unfavorable characteristics such as high swell potential, significant settlement, low bearing capacity, and moisture sensitivity, posing serious challenges to sustainable road construction. Conventional soil stabilization methods, including the use of cement and lime, are not only costly but also contribute significantly to energy consumption and greenhouse gas emissions—especially CO₂—making them less compatible with sustainable development principles. In this context, recycling solid urban and industrial wastes serves not only as an intelligent alternative to traditional binders but also as an effective step toward reducing waste volume, conserving natural resources, and advancing the circular economy. This study investigates the application of a geopolymer system combining waste glass powder (WGP)—a silica-rich urban waste—and calcium carbide residue (CCR)—a by-product of acetylene gas production—for the stabilization of clay soil. A series of geotechnical tests and microstructural analyses were conducted to evaluate the performance of this composite. Results showed that soil samples stabilized with 15% WGP and 7% CCR exhibited the highest improvement in mechanical properties. Microscopic analyses confirmed the formation of geopolymeric gels (C-A-S-H and C-S-H), which enhanced structural densification and reduced effective porosity. This research holds dual significance: from both a technical-mechanical and an environmental-waste management perspective, as the synergistic use of these two wastes simultaneously addresses geotechnical challenges of soft clay stabilization and environmental concerns related to waste disposal. Therefore, the findings of this study can pave the way for broader utilization of waste-derived materials in sustainable, low-carbon infrastructure projects.