A bioinspired Cu–Fe Prussian blue analogue (PBA) functionalized PTFE membrane (Cu–Fe PBAs@M) is developed for ultra-trace cesium (Cs+) removal, achieving over 99% rejection at 50 ppb concentration under cross-flow filtration. Structural and chemical characterizations confirm uniform incorporation of Cu–Fe PBAs with a tunable Cu: Fe ratio that optimizing adsorption kinetics and membrane permeability. The membrane demonstrates an equilibrium adsorption capacity of ∼42 mg/m2 at trace Cs + levels and maintains >97.5% removal across pH 5–10. Competitive ion studies reveal selective Cs+ capture despite 200-fold excess of common cations, supported by density functional theory showing adsorption energies favoring Cs+ (−5.74 eV). Regeneration via mild acid or water elution sustains removal efficiency above 98% over multiple cycles with negligible metal leaching. Performance validation in real river water and hypersaline brines confirms operational robustness and scalability. This work establishes a scalable membrane platform for selective, high-efficiency radionuclide remediation and resource recovery from complex aqueous environments.