Among various effecting factors, groundwater is commonly known as one of the major triggers for slope failures. Thus, it is great significant of considering the contribution from groundwater seepage in slope stability analysis. In this study, the effect from groundwater seepage are considered as the interaction force (infiltration force) between water and soil materials for static and moment equilibrium analysis. Based on Rigorous Janbu method, the implicit equations are determined for estimating the minimum factor of safety and locating the non-circular critical failure surface. A new metaheuristic algorithm, Improved Radial Movement Optimization (IRMO), was adopted to figure out such complex, nonlinear and constrained optimization problem due to its high precision and stability. The effectiveness of the proposed methodology is validated by four different cases including homogeneous and inhomogeneous slopes from the literature. Comparative studies in different optimization algorithms have been carried out to validate the stability and efficiency of proposed IRMO algorithm accordingly. The results indicate that proposed approaches could acquire a more acceptable and stable result with more efficient way in slope stability analysis considering seepage effect over several existing methods.