Carbon nanotube has been explored as a nanofiller in high performance polymeric membrane for gas separation. In this regard, nanocomposite membrane of polycarbonate (PC), poly(vinylidene fluoride-co-hexafluoropropylene) (PVFHFP), and multiwalled carbon nanotube (MWCNT) was fabricated via phase inversion technique. Poly(ethylene glycol) (PEG) was employed for the compatibilization of the blend system. Two series of PC/PVFHFP/PEG were developed using purified P-MWCNT and acid functional A-MWCNT nanofiller. Scanning and transmission electron micrographs have shown fine nanotube dispersion and wetting by matrix, compared with the purified system. Tensile strength and Young’s modulus of PC/PVFHFP/PEG/MWCNT-A 1–5 were found to be in the range of 63.6–72.5 MPa and 110.6–122.1 MPa, respectively. The nanocomposite revealed 51% increase in Young’s modulus and 28% increase in tensile stress relative to the pristine blend. The A-MWCNT was also effective in enhancing the permselectivity αCO2/N2 (31.2–39.9) of nanocomposite membrane relative to the blend membrane (21.6). The permeability PCO2 of blend was 125.6 barrer; however, the functional series had enhanced PCO2 values ranging from 142.8 to 186.6 barrer. Moreover, A-MWCNT loading improved the gas diffusivity of PC/PVFHFP/PEG/MWCNT-A 1–5; however, filler content did not significantly influence the CO2 and N2 solubility.