A nitrogen-doped carbon microsphere sorbent with a hierarchical porous structure was synthesized via aggregation-hydrothermal carbonization. The Hg⁰ adsorption performance of the nitrogen-doped carbon microsphere sorbent was tested and compared with that of the coconut shell activated carbon prepared in the laboratory. The effect of H₂S on Hg⁰ adsorption was also investigated. The nitrogen-doped carbon microsphere sorbent exhibited superior mercury removal performance compared with that of coconut shell activated carbon. In the absence of H₂S at a low temperature (≤ 100 °C), the Hg⁰ removal efficiency of the nitrogen-doped carbon microsphere sorbent exceeded 90%. This value is significantly higher than that of coconut shell activated carbon, which is approximately 45%. H₂S significantly enhanced the Hg⁰ removal performance of the nitrogen-doped carbon microsphere sorbent at higher temperatures (100–180 °C). The hierarchical porous structure facilitated the diffusion and adsorption of H₂S and Hg⁰, while the nitrogen-containing active sites significantly improved the adsorption and dissociation capabilities of H₂S, contributing to the generation of more active sulfur species on the surface of the nitrogen-doped carbon microsphere sorbent. The formation of active sulfur species and HgS on the sorbent surface was further confirmed using X-ray photoelectron spectroscopy and Hg⁰ temperature-programmed desorption tests. Density functional theory was employed to elucidate the adsorption and transformation of Hg⁰ on the sorbent surface. H₂S adsorbed and dissociated on the sorbent surface, generating active sulfur species that reacted with gaseous Hg⁰ to form HgS.