ISoil slopes are inherently heterogeneous, and their seismic stability is strongly influenced by soil layering, strength contrast, and layer thickness. This study investigates the stability of homogeneous and two-layered non-homogeneous slopes under static and seismic loading using the strength reduction finite element method in OPTUM G2. Stability charts are developed for slope angles of 25°, 35°, and 45°, upper-layer thickness ratios (T/D = 0.2–0.8), and combinations of fine- and coarse-grained soils, with pseudo-static loading applied using Kh = 0.1 and Kv = 0.05. Results show that seismic loading reduces safety factors by approximately 20–35%, while placing stronger fine-grained soil in the foundation increases stability by 25–40%. Increasing friction angle enhances stability by 60–120%, particularly for steep slopes and seismic conditions, whereas increasing cohesion improves stability only up to a critical ratio (c₁/c₃ ≈ 1.2), beyond which gains are negligible (<3%). Coarse-grained soils predominantly exhibit translational failure, while fine-grained soils show rotational failure, with seismic loading shifting stability control from cohesion to friction. The novelty lies in the unified stability and failure mode charts quantifying layer sequence, thickness ratio, and coupled seismic effects for stratified slopes.