The application of pure chitosan film (CS) is limited by its high brittleness, strong hydrophilicity, and inadequate antioxidant capacity. To address these drawbacks, aqueous suspensions of lignin nanoparticles (LNPs) and quercetin-encapsulated lignin nanoparticles (QT-LNPs) were prepared using the anti-solvent method. Subsequently, a series of nanocomposite films were fabricated by blending these suspensions with chitosan solution at volume ratios of 5% and 10%, separately. The physicochemical properties and antioxidant activities of the resulting films were systematically evaluated. The results demonstrated that LNPs and QT-LNPs with average particle sizes of 125 nm and 245 nm, respectively, were successfully obtained and well dispersed within the chitosan matrix. Fourier transform infrared spectroscopy, X-ray diffraction, and thermal analysis confirmed the formation of hydrogen bonding interactions between the nanoparticles and the chitosan matrix. Such interactions reduced the crystallinity of composite films while improving their thermal stability. Additionally, the thickness, water content, and swelling degree of the composite films were significantly reduced, while a slight increase in water solubility was observed. Both water vapor and oxygen barrier properties of the composite films were remarkably improved. The tensile strength of the QT-LNPs-10% film increased to 147.08% of that of CS, reaching a maximum value of 39.83 MPa; meanwhile, the elongation at break of the film was enhanced by up to 75.68%. Antioxidant measurements showed that the QT-LNPs-10% film achieved maximum DPPH and ABTS free radical scavenging rates of 90.20% and 93.43%, respectively. In summary, this film exhibited superior comprehensive performances and provides a theoretical basis for the modification of active green food packaging films.