[N,N′-Bis(salicylidene)-1,2-phenylenediamine]zinc(II) (ZnC) exhibits unexpected properties as a photoinitiator or additive for both free-radical photopolymerization reactions and in situ formation of Zn-based fillers under light activation and aerated conditions. The ZnC/2,2-dimethoxy-2-phenylacetophenone (DMPA) and ZnC/N-methyldiethanolamine (MDEA) couples are characterized by remarkable properties: (i) a photoinitiating efficiency for the radical polymerization of an acrylate matrix under air higher than that of a reference Type I photoinitiator such as DMPA (final conversion of ∼30–45% vs. 15%) and therefore a good ability to overcome the oxygen inhibition effect and (ii) a never reported in situ formation of Zn-based fillers (100 μm thick sticks) or composites. The photochemical properties of the ZnC are investigated by fluorescence and UV-visible spectroscopy and Electron Spin Resonance (ESR). The photodecomposition of ZnC under air is governed by either an addition of peroxyl radicals onto ZnC when associated with DMPA, or a H-abstraction mechanism when combined with MDEA. When using a ZnC/MDEA/silver salt photoinitiating system, a highly efficient polymerization of the acrylate matrix under air and a concomitant in situ production of Ag(0) NPs are observed.