A novel hybrid nanocomposite has been successfully fabricated for persulfate (S₂O₈²⁻) detection. It can be easily prepared by grafting silicomolybdate (SiMO) and poly(3,4-ethylenedioxythiophene) (PEDOT) on multi-walled carbon nanotubes (MWCNT) to form a SiMO–PEDOT/MWCNT hybrid composite. The SiMO–PEDOT film formation is initiated through the electropolymerization of EDOT monomers. The monomers are firstly electropolymerized to form the positive PEDOT and then the positive polymers are attractive to the negative SiMO, resulting in the electrocodeposition on the electrode surface. It shows three significant redox couples and the redox peak currents can be enhanced by using a MWCNT-modified electrode. Morphological features were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrode shows good activity towards S₂O₈²⁻ reduction with low overpotential (E_pc = 0 V). Amperometric response provides a linear range of 1–3333 μM with sensitivity of 2928.9 μA mM⁻¹ cm⁻², a detection limit of 1 × 10⁻⁶ M (S/N = 3), and response time of 2.3 s. The SiMO–PEDOT/MWCNT electrode can effectively analyse S₂O₈²⁻ due to its low overpotential, high sensitivity, good stability, fast response, and low cost.