Herein, flexible, strong and optically tunable nano-CuO-loaded poly(vinyl alcohol) (PVA) composite films were fabricated by means of solution casting approach. The nanocomposite films were characterized using advanced analytical techniques. A small loading with CuO nanofiller resulted in prominent modifications of structural and optomechanical attributes of PVA-based nanocomposites. The comprehensive band structure and mechanical investigations of the prepared samples have been reported. The loading with just 0.5 wt% CuO nanofiller in PVA resulted in significant changes in direct band gap (5.29 to 3.16 eV), indirect band gap (4.91 to 2.88 eV), Urbach energy (0.22 to 1.12 eV), dispersion energy (1.45 to 1.92 eV), oscillator energy (5.74 to 3.25 eV), tensile strength (25.6 to 42.2 MPa), Young's modulus (144 to 215 MPa), elongation at break (152.4 to 206.1%) and the flexural strength (4.1 to 32.2 MPa). The optical band gap calculated using Tauc's relation, Wemple and DiDomenico single oscillator model and dielectric loss approach resulted in nearby values. Various theoretical models were employed to validate the experimentally determined Young's moduli values. A possible application of such nanocomposite films might be in optoelectronic devices.