Sensitive yet rapid methodologies for efficient recognition of toxic heavy metals, like Hg2+, would avert the poisonous impacts of these elements on the environment and human health. Herein, we present a highly selective fluoresceine-based fluorogenic probe FP for Hg2+ recognition with quick response, an impressive LOD of 67.1 nM, high sensitivity, and a linear emission increment relationship with Hg2+ concentration (0–20.0 μM). FP could specifically recognize Hg2+ and it exhibited a 250-fold emission enhancement at 515 nm to Hg2+, but no response to other common cations. The mechanism for FP-Hg2+ was completely examined through FTIR, 1H NMR, TOF-MS, and density functional theory (DFT) calculations. To examine naked-eye recognition of Hg2+, the FP-coated silica plates, and cotton swabs were productively manufactured for the sensing of Hg2+. Besides, FP was able to recognize Hg2+ in biological systems with excellent efficiency. Overall, ultra-fast recognition property of FP for Hg2+, high sensitivity, and selectivity of FP against Hg2+ could be conveniently utilized to prevent the toxicity of Hg2+.