<p>Mercury contamination poses a profound threat to both environmental integrity and human well-being due to its extreme toxicity and strong bioaccumulative properties. Consequently, there is an increasing imperative for detection methodologies that exhibit exceptional sensitivity, selectivity, and efficiency in identifying mercury ions (Hg²⁺) with rapid response times. Among the diverse array of analytical techniques, fluorescent and colorimetric sensors have emerged as highly promising due to their operational simplicity, remarkable sensitivity, and capability for real-time monitoring. This review delves into recent advancements in these sensing modalities, with a particular emphasis on cutting-edge detection mechanisms, nanomaterial-enhanced strategies, and innovative probe architectures. Finally, this review critically examines the prevailing challenges and explores future perspectives for these technologies in pivotal domains such as environmental surveillance, food safety, and biomedical diagnostics.</p>