Composite solid-state electrolytes have received significant attention due to their combined advantages as inorganic and polymer electrolytes. However, conventional ceramic fillers offer limited ion conductivity enhancement for composite solid-state electrolytes due to the space-charge layer between the polymer matrix and ceramic phase. In this study, we develop a ferroelectric ceramic ion conductor (LiTaO₃) as a functional filler to simultaneously alleviate the space-charge layer and provide an extra Li⁺ transport pathway. The obtained composite solid-state electrolyte comprising LiTaO₃ filler and poly (vinylidene difluoride) matrix (P-LTO15) achieves an ionic conductivity of 4.90 × 10⁻⁴ S cm⁻¹ and a Li⁺ transference number of 0.45. The polarized ferroelectric LiTaO₃ creates a uniform electric field and promotes homogenous Li plating/stripping, providing the Li symmetrical batteries with an ultrastable cycle life for 4000 h at 0.1 mA cm⁻² and a low polarization overpotential (~50 mV). Furthermore, the solid-state NCM811/P-LTO15/Li full batteries achieve an ultralong cycling performance (1400 cycles) at 1 C and a high discharge capacity of 102.1 mAh g⁻¹ at 5 C. This work sheds light on the design of functional ceramic fillers for composite solid-state electrolytes to effectively enhance ion conductivity and battery performance.