Ionic conduction plays a vital role in biological systems, energy storage and ionotronic devices. Polyelectrolyte elastomers have attracted growing interest as solid-state single-ion conductors due to their inherent ion selectivity, leakage-free nature and mechanical elasticity. However, existing polyelectrolyte elastomers have relatively low ionic conductivity (~10−3 mS cm−1), limiting their applicability as efficient ionic conductors. Here we present a materials design approach that boosts conductivity and preserves leakage-free operation by introducing a solid-state additive that combines two key characteristics: a high dielectric constant to increase dissociated ion density (n" role="presentation"> n ) and a plasticizing effect to enhance ion mobility (μ" role="presentation"> μ ). Demonstrated with succinonitrile, this approach increases conductivity by over two orders of magnitude at room temperature across both polycationic and polyanionic systems, further enhancing elasticity. By elevating conductivity across diverse polyelectrolyte networks, this work demonstrates a versatile route to achieve stable and efficient ion transport for next-generation solid-state single-ion conductors.