Groundwater in open-pit mines can significantly influence mining operations, affecting both safety and productivity. A thorough understanding of groundwater conditions and their impact on slope stability is essential for optimizing mine design and ensuring operational efficiency. This study investigates the effects of groundwater on the slope stability of the western pit in the Sangan iron ore mine through detailed numerical modeling. The graphical model revealed that in the tenth year of mining operations, the safety factors in the lower benches fell below 1.3, indicating potential instability based on the Mohr–Coulomb failure criterion. This instability poses a significant risk to the structural integrity of the mine. Further analysis demonstrated that reducing pore pressure could substantially increase the factor of safety, thereby mitigating the risk of slope failure. To address this critical issue, a comprehensive dewatering program was meticulously designed, modeled, and implemented to effectively reduce or eliminate pore pressure, ultimately enhancing pit slope stability. The validity of the numerical model was rigorously confirmed through subsequent analysis, demonstrating its reliability as a predictive tool for groundwater flow and slope stability assessment in similar mining environments. This study underscores the crucial importance of incorporating groundwater management into the design and operational planning of open-pit mines to ensure long-term stability and safety.