Agri-food waste valorization is critical for advancing sustainable packaging solutions. Citrus processing generates large amounts of peel residues that are often discarded, despite being rich in valuable biopolymers. This study presents a fully integrated, zero by-product valorization strategy for the fabrication and characterization of pectocellulosic nanocomposite films derived from orange peel (OP) biomass. Orange peel extract (OPE) was prepared and used for the biosynthesis of ZnO nanoparticles (NPs), while cellulose was obtained after the depectinization reinforced the pectin-rich supernatant used as the film-forming matrix (0–15% w/w). The optimized formulation containing 5% cellulose enhanced tensile strength by approximately 103% and reduced water vapor permeability by about 12.5% compared to the control, while maintaining structural homogeneity. Higher cellulose loading (≥10%) induced pore formation and compromised barrier and biological performance. Incorporation of ZnO NPs (1–5% w/w) into the optimized matrix further improved stiffness (YM = 163.9 MPa), improved UV-shielding capacity, antimicrobial activity (inhibition zones up to 16.0 mm), and antioxidant performance (98.2% ABTS inhibition). Biodegradation remained statistically unaffected by ZnO incorporation, with films retaining 29–35% degradation within 33 days. Overall, this work demonstrates the transformation of OP waste into multifunctional biodegradable active packaging materials, reinforcing circular bioeconomy principles.