This paper presents a study on the probabilistic seismic hazard analysis of a slope at a given site in a specified exposure time. This study is part of the long-term performance assessment of a slope. For the long-term performance assessment, the factors that may lead to failure of the slope over time, such as the seismic ground motion, spatial variability of soil strength, and fluctuation of groundwater level, should be considered. Here, the earthquake-induced ground motion at a given site in a specified exposure time is simulated by a random variable based on the USGS National Seismic Hazard Maps, the spatial variability of the shear strength of the soil is modelled by a random field, and the fluctuation of the groundwater level is modelled by a random variable. To estimate the total failure probability of the slope at a given site in a given exposure time, a recently developed sampling technique is adopted for the propagation of uncertainties, and a 2D finite difference program is used as the deterministic model for the slope stability analysis. To demonstrate the proposed approach, an illustrative example of a two-layer earth slope is studied; and, a parametric study is undertaken to investigate how the long-term performance of the slope is affected by the influencing factors. With the results presented, the versatility and effectiveness of the proposed probabilistic framework are illustrated.