Polypyrrole Sn(IV) phosphate, an organic–inorganic composite cation-exchanger was synthesized via sol-gel mixing of an organic polymer, polypyrrole, into the matrices of the inorganic precipitate of Sn(IV) phosphate. The physico-chemical properties of the material were determined using Atomic Absorption Spectrometry (AAS), CHN elemental analysis (inductively coupled plasma mass spectrometry, ICP-MS), UV–VIS spectrophotometry, FTIR (Fourier Transform Infra-Red), SEM (Scanning Electron Microscopy), TGA–DTA (Thermogravimetric Analysis–Differential Thermal Analysis), and XRD (X-ray diffraction). Ion-exchange behavior was observed to characterize the material. On the basis of distribution studies, the material was found to be highly selective for toxic heavy metal ion Mn2+. Due to its selective nature, the material was used as an electroactive component for the construction of an ion-selective membrane electrode. The proposed electrode shows fairly good discrimination of mercury ion over several other inorganic ions. The analytical utility of this electrode was established by employing it as an indicator electrode in electrometric titrations for Mn(II) in water.