A thorough investigation was conducted on poly(lactic acid) (PLA) nanocomposites based on silver (Ag) nanoparticles (NPs) as metallic nanofillers (from 0.5 to 5.0 wt%). The PLA Ag nanocomposite films were developed using the cast film extrusion technique. Gel permeation chromatography and intrinsic viscosity measurements revealed that cast film extrusion induced a significant reduction in the number average molecular weight of PLA, attributed to thermomechanical degradation, whereas the presence of NPs assisted and promoted the stability of the PLA films without further degradation. Proton nuclear magnetic resonance spectroscopy and Fourier-transform infrared spectroscopy confirmed that the incorporation of Ag NPs did not induce any changes to the chemical structure of the polymer matrix. Scanning electron microscopy analysis showed an oriented morphology in neat PLA due to extrusion induced flow, whereas the addition of Ag NPs increased the surface heterogeneity. Differential scanning calorimetry results indicated that Ag NPs acted as nucleating agents, enhancing the degree of crystallinity of PLA. Complex segmental dynamics was revealed by dielectric spectroscopy, with the main segmental relaxation being accelerated and exhibiting an almost monotonic lowering of the cooperativity level with Ag NP loading. Partial densification of the polymer around the NPs and an increase in the free polymer volume away from them was expected. The mechanical performance was evaluated through tensile and flexural tests, where the presence of NPs enhanced the stiffness and strength of the samples, while the ductility was reduced. Annealing experiments also enhanced the mechanical performance of the materials. Finally, water contact angle measurements showed that the surface hydrophobicity was increased. Thus, in this study, PLA nanocomposites based on metal NPs produced via cast film extrusion were developed for advanced industrial applications; such nanocomposites are reported experimentally for the first time.