The study focused on the probability-based design of reinforced veneer cover systems of municipal solid waste landfills against sliding failure. This study uses a composite column model to consider strain compatibility for estimating the tensile loads in the geogrid reinforcement. Monte Carlo simulations are adopted to present an efficient reliability analysis. The variability associated with unit weight (γ), friction angle (ϕ), stability number (c/ γH), Poisson’s ratio of cover soil (υ), the elastic modulus of cover soil, stiffness of geogrid (Kt), and the stiffness ratio of cover soil and geogrid (Kc/Kt) is considered in this study. The formulation is presented to obtain the reliability index against sliding failure (βsli). The values of reliability indices (βsli) are obtained for reinforced as well as unreinforced veneer systems. It is observed that an increase in the stiffness of the geogrid reinforcement (Kt) increases the stability of the cover system. The maximum allowable thickness of cover soil (h) increased significantly by 162.50, 137.50, 134.78, 130.43, and 126.09% for the stiffness ratios (Kc/Kt) of 0.5, 1.0, 1.5, 2.0, and 2.5, respectively, when L/H ratio increases from 2.1 to 3.3. The maximum allowable thickness of cover soil (h) by targeting the reliability index (βsli) ≥ 3.0 is provided in the form of design charts for different values of stiffness ratios (Kc/Kt) which ensures the safety of the reinforced veneer cover system against sliding failure. © 2023, The Author(s), under exclusive licence to Indian Geotechnical Society.