The complex bis(acetylacetonato)platinum(II) is inactive in the dark but forms a highly reactive hydrosilation catalyst upon irradiation with near-UV light. Vinyldimethylsilane is polymerized with it. Poly[(dimethyl)vinylsilane] is the major product; minor components consist of the dimers 1,1,2,3,3-pentamethyl-1,3-disilacyclopentane and 1,1,4,4-tetramethyl-1,4-disilacyclohexane and oligomers. After photoactivation the catalyst remains reactive for an indefinite period of time with hydride and vinyl polymer end-groups, thus the molecular weight of the major product increased from 5500 g/mol (M(w)) shortly after irradiation to 12300 g/mol in six months due to end-linking of polymer chains. Photoactivation of the catalyst and the subsequent step polymerization reaction are unaffected by dissolved air.