We report a polysiloxane based single-ion conducting polymer electrolyte (SIPE) synthesized via a hydrosilylation technique. Styrenesulfonyl(phenylsulfonyl)imide groups were grafted on highly flexible polysiloxane chains followed by lithiation. The highly delocalized anionic charges in the grafted moiety give rise to weak association with lithium ions in the polymer matrix, resulting in a lithium ion transference number close to unity (0.89) and remarkably high ionic conductivity (7.2 × 10⁻⁴ S cm⁻¹) at room temperature. The high flexibility arising from polysiloxane enables the glass transition temperature (T_g) to be below room temperature. The electrolyte membrane displays high thermal stability and a strong mechanical strength. A coin cell assembled with the membrane comprised of the electrolyte and poly(vinylidene-fluoride-co-hexafluoropropene) (PVDF-HFP) performs remarkably well over a wide range of temperatures with high charge–discharge rates.