A biodegradable and transparent flexible food packaging material using a nanocellulose-based biocomposite was developed. The formulation consists of nanocellulose (NC), chitosan (CS), gelatin (Gel), citrate ester (CE), and glycerol (GL), carefully designed to enhance mechanical properties, flexibility, and barrier performance while maintaining full biodegradability and transparency. Nanocellulose provides structural integrity and an ultra-low oxygen transmission rate (OTR), while chitosan contributes antimicrobial activity and enhances the composite’s moisture barrier properties. Gelatin improves film-forming ability and elasticity, ensuring a uniform and flexible structure. The combination of citrate ester and glycerol acts as effective plasticizers, reducing brittleness and improving overall mechanical performance. Barrier performance tests demonstrated exceptional oxygen and moisture resistance, with an OTR of 0.2–0.5 cc/m²·day (23°C, 50% RH) and WVTR of 1.5–2.3 g/m²·day (38°C, 90% RH). The strong oxygen barrier effectively reduces oxidative degradation, while the moisture resistance helps maintain food quality. Food preservation studies showed that fresh produce packaged in this biocomposite film maintained its freshness for up to 2 weeks at room temperature. Furthermore, we successfully applied this formulation to various packaging films using a roll-to-roll (R2R) processing technique, demonstrating its scalability and commercial viability. Through multiple optimizations, the material has been further refined and is now suitable for use in paper-based packaging applications. This advancement expands the potential of bio-based nanocomposites in eco-friendly packaging, offering a high-performance and sustainable solution for food preservation while reducing environmental impact.