The detection of heavy metal ions in living systems and aqueous environments has attracted significant attention in recent years, especially the detection of mercury, one of the most toxic heavy metals on Earth. To reduce mercury’s lethal effects on the human body, animals, and marine life trace amounts of mercury species can be detected by using classical spectroscopic techniques for example atomic absorption and emission spectroscopy, high-performance liquid chromatography, and inductively coupled plasma mass spectrometry. However, because those techniques are time-consuming and expensive, fluorescence analysis, which offers high selectivity and sensitivity, has emerged as a suitable alternative for detecting mercury species. In the work presented here, a new BODIPY -based fluorescent probe functionalised with a phenylhydrazine unit was designed and synthesised for the selective and sensitive detection of mercury species. The probe’s detection limit was determined to be 29 nM, and the probe could detect mercury species in living cells without any changes in cell morphology.