Degradation caused by processing and usage conditions, along with the rapid increase in industrial waste, has become a major concern that affects the durability and environmental sustainability of natural products, including natural rubber (NR). To address these challenges, this study explored the potential of utilizing gamma-irradiated mangosteen peel powder (MPP) as a bio-filler to replace conventional chemical antioxidants in natural rubber latex (NRL) films, with varying MPP contents (0–9 parts per hundred rubber (phr)) and gamma irradiation doses (0–40 kGy). The study evaluated the mechanical, morphological, physical, and biodegradability properties of the NRL composites, both before and after exposure to thermal and gamma aging conditions. Based on the results, the addition of gamma-irradiated MPP significantly enhanced degradation resistance under both thermal and gamma aging. Notably, NRL films containing 9 phr of MPP irradiated at 10 kGy had the highest aging coefficients and the least physical changes for both aging conditions. Additionally, biodegradability assessments on samples that had been buried in soil for 8 weeks indicated that weight loss increased with a higher MPP content and gamma irradiation dose, suggesting a synergistic effect of MPP and gamma irradiation in enhancing the biodegradability of NRL films. Overall, based on the findings, the incorporation of gamma-irradiated MPP not only improved the degradation resistance and biodegradability of the NRL films that sufficiently improved durability of the NR products and reduced industrial waste, but also produced an environmentally-friendly bio-filler that offered a sustainable alternative to conventional, hazardous chemical additives used in the rubber and polymer industries.