Landfill leachate contains complex mixtures of organic matter and toxic heavy metals that pose significant environmental and public health risks; therefore, this study aimed to evaluate the potential of Gracilaria changii, a locally available red seaweed, as a low-cost and sustainable biosorbent for zinc (Zn²⁺) and copper (Cu²⁺) removal from real landfill leachate. Batch adsorption experiments were conducted using leachate collected from Jeram Landfill, Malaysia, which was spiked with Zn²⁺ and Cu²⁺ to ensure controlled concentrations, and the effects of key operational parameters including pH (2.5–8.0), biosorbent dosage (5–25 g), and contact time (30–180 min) were systematically investigated using a jar test apparatus at room temperature. The results demonstrated that pH significantly influenced biosorption performance, with maximum removal efficiencies of 71.89% for Zn at pH 2.5 and 44.50% for Cu at pH 5.5. Increasing the G. changii dosage enhanced metal removal due to the greater availability of active binding sites, achieving optimum removals of 99.14% for Zn and 80.75% for Cu at a dosage of 25 g. Adsorption efficiency increased with contact time and reached equilibrium between 150 and 180 min for both metals, indicating favorable biosorption kinetics. Although the study was limited to batch-scale laboratory experiments and focused on two heavy metals, the findings provide strong evidence of the biosorption capability of G. changii under controlled conditions. The use of this seaweed presents practical value as an environmentally friendly and cost-effective alternative to conventional adsorbents, with potential for integration into existing landfill leachate treatment systems. Notably, this study represents the first reported application of Gracilaria changii for Zn and Cu removal from real landfill leachate, offering original and significant insights into seaweed-based biosorption for sustainable wastewater treatment.