Mercury is a neurotoxic heavy metal that threatens to human health and ecosystems. This study examinedthe mercury tolerance and biosorption capacity of the GRAS yeast Saccharomyces cerevisiae BY4741 Growth persisted at 100 ppm but was completely inhibited at 200 ppm; thus, the MIC is bracketed between 100 and 200 ppm. Tolerance assays revealed that the strain BY4741 exhibits a minimum inhibitory concentration (MIC) of ≥ 100 ppm for HgCl₂. Cell viability showed a significant decline (p ≤ 0.05) with increasing mercury concentrations, as determined by the Total Plate Count method. Bioinformatic analysis identified detoxification-related genes (YCF1, YAP1, GSH1, URE2) that were upregulated under HgCl₂ exposure, which are involved in glutathione metabolism, transcriptional regulation, vacuolar efflux, redox homeostasis, and metal ion transport. qRT-PCR confirmed selective activation of these genes, with URE2 displaying the highest induction. Biosorption efficiency reached 49.13% after 24 h of contact time, and X-ray mapping confirmed the accumulation of mercury within the S. cerevisiae biomass. These findings highlight the potential application of S. cerevisiae as a microbial biosorbent for mercury in bioremediation strategies.