Mercury contamination of soils, even at relatively low levels, remains a global environmental and health concern due to its persistence, bioaccumulation, and toxicity. Phytoremediation offers a sustainable and cost-effective strategy, and the addition of organic amendments can improve plant growth and metal uptake. This study investigated the use of chicken manure compost to enhance mercury removal by Brachiaria dyctioneura, a tropical forage species with high adaptability and biomass production. Two soils with initial mercury concentrations of 106.07 ± 13.41 μg/kg and 672.234 ± 74.59 μg/kg were amended with chicken manure at 1:4 and 3:4 ratios (manure:soil). Physicochemical properties, organic carbon, nitrogen, phosphorus, and metal contents were characterized. Seeds of B. dyctioneura (1 g per experimental unit) were sown with five replicates per treatment. After 30 days, plants were separated into roots and shoots for mercury determination using EPA Method 7473 with a RA-915LAB Direct Mercury Analyzer. Results indicated that lower amendment levels enhanced mercury accumulation in shoots, favoring aerial translocation, while higher doses increased retention in roots and reduced translocation. For Soil 1, mercury concentrations were 3.49–24.92 μg/kg in roots and 10.32–14.63 μg/kg in shoots, whereas in Soil 2 values reached 13.44–191.53 μg/kg in roots and 67.59–90.47 μg/kg in shoots. These results suggest that amendment dosage significantly influences mercury partitioning in plants. The findings highlight the potential of B. dyctioneura as a promising species for mercury phytoremediation, with chicken manure compost serving as an effective amendment to optimize remediation performance.