This study investigates the durability of cassava starch-stabilized lateritic soils subjected to cyclic wet–dry loading, using unconfined compressive strength (UCS) and indirect tensile strength (ITS) retention as key durability measures. Lateritic soils, widely used in tropical subgrade construction, suffer strength loss due to moisture fluctuations. Conventional stabilizers like cement and lime, although effective, have significant environmental drawbacks. Cassava starch, a biodegradable and abundant biopolymer, offers a sustainable alternative with promising soil-binding properties. Twelve mix designs, incorporating varying proportions of lateritic soil, cassava starch (0–10%), and water-to-solids ratio (12–16%), were prepared and cured for 28 days before undergoing 12 wet–dry cycles to simulate environmental stress. UCS retention ranged from 69.68% to 91.24%, and ITS retention from 71.79% to 92.91%, with the best-performing mix surpassing ASTM and AASHTO durability criteria and Nigerian subgrade strength requirements. Scheffé’s (3,2) mixture regression models accurately predicted durability outcomes, achieving R² values above 99% and passing F-tests for model adequacy at a 5% significance level. These findings confirm cassava starch’s effectiveness in enhancing the mechanical resilience and moisture durability of lateritic soils, supporting its application as a green stabilizer for sustainable infrastructure. The study presents a validated, data-driven framework for optimizing bio-based soil stabilization, advancing eco-friendly geotechnical practices and climate-resilient road construction.