<p>The growing demand for sustainable materials has accelerated the shift toward eco-friendly composites as substitutes for synthetic alternatives. This study reports the development of a vinyl ester-based biocomposite reinforced with silane- and alkali-treated papaya leaf stem fibers and marine-derived chitin biopolymer. By integrating agricultural waste and marine biomass, the work addresses waste valorization and resource sustainability. Composite formulations were prepared by varying chitin content at a fixed fiber loading, and their mechanical, flammability, and machinability characteristics were evaluated. The optimized composition achieved significant improvements in strength, drilling precision, and flame resistance due to enhanced interfacial bonding between the chemically modified fiber, filler, and matrix. The findings demonstrate that chemical surface modification is an effective strategy to overcome interfacial limitations, enabling lightweight, machinable, and environmentally friendly composites. The study highlights a unique approach that combines marine- and plant-based wastes into value-added materials with promising applications in automotive interiors, construction panels, and sustainable consumer products.</p>