Mercury (Hg) is one of the most toxic and persistent environmental pollutants, entering ecosystems in large quantities through both natural and anthropogenic activities. This heavy metal poses a serious threat to the health of aquatic and terrestrial ecosystems due to its ability to transform into methylmercury—the most toxic form of mercury—and its high potential for biomagnification in food webs. Findings indicate that although the Minamata Convention has taken effective steps to reduce mercury emissions, climate change, permafrost thaw, and land-use changes can delay the recovery process of ecosystems. Furthermore, plants play a major role in the global mercury cycle by absorbing mercury from the atmosphere, accounting for 60 to 90 percent of mercury deposition in terrestrial ecosystems. The present article aims to review the sources, biogeochemical cycles, toxicity mechanisms, effects of mercury on aquatic and terrestrial organisms, biomagnification consequences, and monitoring and management strategies for mercury pollution in ecosystems. Critical knowledge gaps remain in understanding plant-level mercury uptake, the synergistic effects of climate change on methylation, and the integration of socioeconomic scenarios into risk assessment models. Addressing these challenges through enhanced international cooperation, capacity building in developing countries, and the adoption of cost-effective remediation technologies will be key to achieving the ambitious goals of the Minamata Convention and ensuring sustainable ecosystem recovery.