Photochemically　mediated　atom　transfer　radical　polymerization　of　vinyl　monomers　is　successfully　activated　by　ecofriendly　heterogeneous　mesoporous　graphitic　carbon　nitride　(mpg-C3N4).　This　method　pertains　to　the　use　of　mpg-C3N4　as　photoactivator　for　reduction　of　initially　loaded　copper(II)　species,　thus　promoting　the　in　situ　formation　of　the　copper(I)　species.　The　controlled　nature　of　the　polymerizations　in　both　natural　sunlight　and　UV-light　irradiation　at　ambient　temperature　is　confirmed　by　the　good　agreement　of　the　kinetics　of　the　polymerization　with　theoretical　values.　The　light　on-off　experiments　demonstrate　that　polymerizations　are　clearly　initiated　and　moderated　by　either　UV　light　or　sunlight.　Photochemically　mediated　atom　transfer　radical　polymerization　of　vinyl　monomers　is　successfully　activated　by　eco-friendly　heterogeneous　mesoporous　graphitic　carbon　nitride　(mpg-C3N4)　under　UV　light　or　sunlight.　The　light　on-off　experiments　demonstrate　that　polymerizations　are　clearly　initiated　by　mpg-C　3N4,　copper(II)　bromide,　and　ethyl-alpha-bromoisobutyrate　as　photoactivator,　catalyst,　and　initiator,　respectively,　which　produces　well-defined　polymers　in　a　controlled　manner.　©　2014　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim.