To address the limitations of earth pressure theory-based design for geosynthetic-reinforced soil (GRS) segmental walls, which is often relatively conservative and unable to simultaneously optimize lateral deformation and carbon emissions, an analytical method for predicting lateral deformation of GRS segmental walls with a life cycle assessment (LCA) framework was proposed. The analytical method considered the complex interactions among facing blocks, geosynthetic reinforcements, and backfill soil. By using multi-objective optimization techniques, an optimized design methodology for GRS segmental walls was developed to achieve a balanced trade-off between lateral deformation and carbon emissions. Validation using practical engineering case demonstrates that the optimized design methodology enables rapid calculation and is suitable for practical application. Lateral deformation can be reduced while maintaining equivalent carbon emissions by optimizing reinforcement length and spacing. The optimal reinforcement length increases with wall height: For walls lower than 5 m, a reinforcement length equal to 0.6 times the wall height is recommended, whereas for taller walls, a length of 0.7 times the wall height is advised.