Water pollution caused by landfill leachate, which contains high concentrations of heavy metals and organic contaminants, poses a serious environmental threat. Among the potential remediation strategies, phytoremediation using Miscanthus x giganteus (giant miscanthus) has gained attention due to its strong resistance to harsh conditions and its capacity to accumulate heavy metals. This study evaluates the effectiveness of Miscanthus x giganteus in treating landfill leachate, with a focus on removing key pollutants such as zinc (Zn), nickel (Ni), and copper (Cu) by simulating wetland conditions. A pilot-scale experiment conducted at the Grebača landfill site assessed the plant’s ability to enhance metal bioavailability, stabilize contaminants, and limit their mobility within the leachate system. The results demonstrated that Miscanthus x giganteus effectively mobilized Zn and Ni through rhizospheric activity, whereas Cu remained largely immobile, indicating potential for phytostabilization. Sequential extraction analysis further confirmed that the plant significantly reduced the mobile fractions of Zn and Ni in the soil, highlighting its dual role in both phytoremediation and phytostabilization. These findings suggest that Miscanthus x giganteus offers a sustainable and cost-effective approach to landfill leachate treatment, serving as a viable alternative to conventional methods. By integrating this nature-based solution into industrial and municipal waste management, it promotes environmental sustainability while enhancing remediation efficiency.