This study aimed to enhance the outdoor performance and thermal properties of wood-plastic composites (WPCs) by incorporating of nanoparticles (NPs). Titanium dioxide (TiO2) was selected as one of the preferred NPs and was added to the matrix in concentrations up to 10%. This addition improved the mechanical properties of WPCs due to the high interaction between TiO2 and the composite components. Furthermore, the high reflectivity properties of TiO2 improved the surface color stability of WPCs. Even under intensive UV light exposure, the surface color changes in WPCs containing TiO2 were more moderate compared to control samples. Microscopic analysis indicated that TiO2 NPs significantly reduced crack formation. Although surface erosion was not completely inhibited, it was reduced. The condensation cycle of weathering weakened the bonds between the wood and polymer, leading to mechanical losses. Scanning electron microscopy (SEM) images revealed micro-cracks, which explained the decreased mechanical properties of reinforced WPCs. However, the decrease was limited to 0.46% for composites containing 5% TiO2. The TiO2 NPs also acted as a thermal barrier, retarding thermal degradation, which occurred more moderately compared to controls. Additionally, the fire performance of reinforced WPCs was enhanced by TiO2 NPs, which improved char formation and increased the limit oxygen index (LOI) values to 25.9% O2.