Sustainable food packaging materials are becoming increasingly important as society faces growing concerns about environmental pollution and food safety associated with non-biodegradable plastics. However, many existing antibacterial films either lack stability under humid conditions or rely on toxic chemical additives, which compromise their safety and environmental compatibility. This challenge highlights the urgent need for biodegradable, water-resistant, and antimicrobial materials suitable for direct food-contact applications while maintaining strong mechanical performance. To address this issue, this study developed an eco-friendly and biocompatible thin film based on polyvinyl alcohol (PVA), tannic acid (TA), and ferric ions (Fe³⁺). The film was prepared through a simple crosslinking reaction between TA and Fe³⁺ within the PVA matrix, forming a stable coordination network that enhances mechanical strength, hydrophobicity, and antibacterial activity. Antibacterial performance was evaluated using inhibition zone and colony-forming unit (CFU) assays against Escherichia coli and Staphylococcus aureus. In addition, food preservation experiments using apple and toast samples were conducted to assess the film’s ability to extend shelf life under different storage conditions. Lastly, the results showed that the PVA/TA/Fe³⁺ film exhibited excellent antibacterial efficiency, achieving more than 80.67% ± 5.90% bacterial inhibition, along with strong resistance to moisture. Food samples stored with the film remained visually fresh for up to five days longer than untreated controls. These findings indicate that the PVA/TA/Fe³⁺ composite film has strong potential as a sustainable and effective alternative to conventional plastic packaging materials.