Accurate and sensitive detection of palladium (Pd) is essential for both environmental and human health applications. This paper describes a triphenylphosphine (PPh₃)-assisted highly sensitive fluorescent chemosensor for ratiometric detection of Pd²⁺ concentrations up to 300 nM with an LOD of 1 nM. During the detection, PPh₃ plays a crucial role in improving the sensitivity of this chemosensor. The chemosensor also has suitable water-solubility which allows detection of Pd²⁺ in solution. Our studies show that it exhibits excellent selectivity toward Pd²⁺ and undergoes a color change from colorless to yellow to allow visual detection of Pd²⁺. Besides detection in solution, this chemosensor also shows great potential as an imaging reagent to detect Pd²⁺ as low as 0.03 ppm in diverse cells.