Polystyrene (PS) has been extensively utilized in packaging, consumer products, and medical applications; however, its susceptibility to ultraviolet (UV) radiation limits its long-term performance and environmental stability. The accelerated photodegradation of PS films under UV irradiation was examined in this study, with an emphasis on the protective function of melamine Schiff base derivatives. Three melamine Schiff base isomers derived from para-, ortho-, and meta-hydroxybenzaldehyde were synthesized and incorporated at low loadings into PS films. Weight loss measurements, Fourier-transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, microscopy, and atomic force microscopy were used to assess the films’ degradation behavior after exposure to continuous UV light for up to 300 h. The development of carbonyl bands in FTIR spectra indicated oxidative chain scission, whereas morphological examinations revealed significant surface roughness and cracking. PS films containing melamine derivatives, on the other hand, showed improved resistance to photodegradation. PS films containing the para-substituted compound exhibited smoother surface morphology and tensile and flexural strengths of 29.8 MPa and 41.5 MPa, respectively, indicating the highest stabilization efficiency. The dual functionality of melamine Schiff bases, which combines UV absorption with radical scavenging and peroxide decomposition, is responsible for this improved performance. These results demonstrate the potential of melamine-based additives as multifunctional photostabilizers that offer high efficiency and structural tunability at low concentrations. This study facilitates the development of advanced UV-resistant materials and offers fresh perspectives on polymer stabilizing techniques.