Solid-state polymer electrolytes (SPEs) possess several favorable properties, such as high flexibility, easy processability, and better safety for batteries. Thus, SPEs are attracting considerable attention for the development of safer Li ion batteries. However, SPEs typically lack the required ionic conductivity for improved Li⁺ transportation. Therefore, suitable fillers are often used to prepare composite polymer electrolytes (CPEs) with improved ionic conductivity. In this direction, a novel CPE with increased electrochemical stability and durability was prepared by incorporating highly porous Zr-based metal–organic frameworks (MOFs), herein referred to as ZR8, as fillers in poly(ethylene oxide) (PEO)/Li salt systems. PEO in the prepared CPE showed low crystallization ratios, and the CPE showed enhanced Li⁺ ion transportation, thereby improving mechanical and fire-retardant properties. It was also able to hinder Li dendrite formation and eventually facilitated efficient transport of Li⁺ ions through the electrolyte. A high specific surface area, the presence of Lewis acid–base sites, and good thermal and chemical stability of the ZR8 filler contributed to the improved electrolyte performance. CPE prepared with 7.5% ZR8 fillers showed a good ionic conductivity of 2.53 × 10⁻⁴ S cm⁻¹ at 30 °C and 1.35 × 10⁻³ S cm⁻¹ at 60 °C and an electrochemical window of ∼5.58 V. The [Li|ZR8-7.5|Li] cell showed an excellent stability in 8000-h operation without any flaw (at 60 °C and a current density of 100 μA cm⁻²). Additionally, the [Li|ZR8-7.5|LFP] cell was able to retain over 80% of its initial capacity (144.9 mA h g⁻¹ at 0.5C) even after 800 cycles.