Here we report preparation and characterization of poly(methyl methacrylate)/silver nanoparticles (PMMA/AgNPs) nanocomposite networks prepared via in situ photoiniferter-mediated photopolymerization (in situ PMP) using tetraethylthiuram disulphide (TED) as photoiniferter and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. Photopolymerization was performed in the presence of allyl methacrylate, as crosslinking agent, and various amount of silver nanoparticles (AgNPs). AgNPs were synthesized via chemical reduction of silver nitrate with t-BuONa-activated sodium hydride in tetrahydrofuran. The degree of monomer conversion (DC%) during polymerization was followed quantitatively via Fourier transform infrared spectroscopy. DC% of nanocomposite networks slightly increased with AgNPs content. Moreover, differential scanning calorimetry results disclosed a decrease in glass transition temperature (𝑇g) of the nanocomposite networks in comparison with the pure polymer network, suggesting the plasticizing effect of AgNPs. Swelling behaviour was also measured in water and ethanol/water (3/1, v/v) solution at 37 ± 1°C after 30 days. The enhanced swelling ratio for nanocomposite networks with increase in the AgNPs content suggested the potential role of AgNPs in photo-crosslinking reactions. The flexural strength and modulus values resulted from three-point bending method revealed an improvement in mechanical properties of the nanocomposites in comparison with pure PMMA networks. The mechanical behaviour observations were rationalized based on the field emission scanning electron microscopy micrographs from the fractured surfaces of the nanocomposite networks. Finally, thermogravimetric analysis showed that while the AgNPs catalyse the degradation in the early stages, they subsequently act as a retardant agent against thermal degradation.