The development of sustainable active bio-composite films based on cassava starch (CS), reinforced with durian rind cellulose nanofiber (CNF) and functionalized with cinnamon essential oil (CEO), was investigated to valorise agricultural waste. The CNF reinforcement was isolated from durian rind using a TEMPO-mediated oxidation method combined with ultrasonication and subsequently incorporated into the starch matrix along with CEO. Response Surface Methodology (RSM) with a Central Composite Design (CCD) was employed to model and optimize the effects of CNF and CEO concentrations on mechanical properties, water barrier performance, and antibacterial activity. The optimization process identified an optimal formulation containing 5% CNF and 2% CEO. This formulation yielded a maximum tensile strength of 10.45 MPa and a Young’s modulus of 188.2 MPa. Furthermore, the simultaneous presence of CNF and CEO effectively enhanced hydrophobicity, reducing the water absorption capacity to 37.5%. The antibacterial modelling revealed broad-spectrum activity, with a more pronounced effect against Gram-positive bacteria. The films exhibited significant inhibition zones against Staphylococcus aureus (up to 2.5 cm) and Escherichia coli (up to 1.0 cm), as demonstrated by the response surface plots. These findings confirm that durian rind-derived CNF combined with CEO is a potent reinforcement for sustainable starch-based active food packaging with tunable mechanical and antimicrobial properties