A composite polymer electrolyte (CPE) based on garnet Li₇La₃Zr₂O₁₂ (LLZO) nanofiber-incorporated PVDF-HFP is reported. The addition of 10 wt% LLZO nanofibers in the developed PVDF-HFP/LiTFSI/LLZO CPE results in an improved ionic conductivity of 9.5 × 10⁻⁴ S cm⁻¹ at room temperature, which is due to the 1D structure of LLZO nanofibers providing continuous Li-ion transport pathways. More importantly, this CPE possesses excellent mechanical strength, making it effective in suppressing Li dendrite growth. In addition, the ceramic nanofiber-incorporated CPE shows an enlarged electrochemical window of 5.2 V vs. Li/Li⁺ in comparison with the one without fillers. Moreover, the cells assembled with this CPE achieve good cycling performance and rate capability. All these favorable features demonstrate that the developed CPE is promising to be used as the electrolyte in the next-generation solid-state Li batteries.