Postharvest microbial spoilage and inadequate packaging significantly compromise food quality during storage, necessitating the development of sustainable and functional packaging materials. A biodegradable bio-composite film (BDF) incorporating ethanolic jamun (Syzygium cumini) seed extract into a polyvinyl alcohol/polyethylene glycol (PVA/PEG) matrix was successfully developed and evaluated for sustainable food packaging applications. The jamun seed extract exhibited strong antimicrobial activity, producing inhibition zones up to 20.62 mm and 20.33 mm against food-borne bacterial and fungal pathogens. GC-MS analysis confirmed the presence of bioactive compounds with known antimicrobial and antioxidant properties, supporting the functional role of the extract in the film matrix. The developed BDF demonstrated significantly enhanced thermal stability, showing only 3% weight loss at 285 °C compared to the control film, along with a higher enthalpy change (-5 W/g), indicating improved heat resistance. Structural characterization confirmed effective incorporation of the extract, while SEM analysis revealed a rough and porous morphology that contributed to accelerated biodegradation. The film exhibited excellent UV-blocking performance, reducing UV transmittance to 15% in the UV-C region, thereby providing effective protection against photo-oxidative food degradation. Notably, the BDF showed pronounced antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Rhizopus spp., demonstrating its potential as an active packaging material. Soil burial tests revealed rapid environmental degradation, with 92.66 ± 0.08% weight loss within 120 days, confirming its eco-friendly nature. Application studies further demonstrated that the jamun-based film effectively extended the shelf life of cherry tomatoes under both ambient and refrigerated conditions. Therefore, this study establishes jamun seed extract-based biodegradable films as a multifunctional, sustainable packaging solution with combined antimicrobial, UV-protective, thermally stable, and biodegradable properties, offering a viable alternative to conventional petroleum-based food packaging materials. This finding suggests that incorporating jamun-based bio-composite films could be a strong, sustainable bio-composite for food packaging applications.