N-vinylcarbazole (NVK) is proposed as an additive for acrylates thermal free radical polymerization (FRP) and epoxy thermal ring opening polymerization (ROP) at room temperature. The new initiating systems are based on a silane/silver salt/N-vinylcarbazole interaction, which ensures good to excellent polymerization. Moreover, the polymerization is much more efficient under air than under argon. The effects of the N-vinylcarbazole, silane, silver salt and monomer structures are investigated. Interestingly, silver nanoparticles Ag(0) are formed in situ. The as-synthesized nanocomposite materials contained spherical nanoparticles homogeneously dispersed in the polymer matrices. Polymers and nanoparticles were characterized by Differential Scanning Calorimetry (DSC), Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectrometry (EDS), Fourier Transform Infrared Spectroscopy (FTIR), and UV-vis spectroscopy. A coherent picture of the involved chemical mechanisms is presented.