In this work, we investigated whether dimethyl malonate could be used as carbene precursor in the cyclopropanation reaction with styrene. Under photochemical conditions, a cobalt(III) carbene radical complex was formed from dimethyl malonate and the formation of the desired cyclopropane was observed. The reaction involves a deprotonation by KOtBu followed by HAT, which can be either performed by benzophenone (an additional HAT reagent) or by the formed malonate radical from [Co III (TPP)(CH(CO2Me)2] (complex 1) upon light irradiation. This provides an attractive method to replace hazardous diazo compounds or halogenated carbene precursors, like iodonium ylides, to form cobalt(III) carbene radical intermediates, especially when conditions can be found that allow catalytic turnover. We are confident that regeneration of [Co III (TPP)Cl] can unlock catalytic pathways using active methylene compounds as stable and readily available carbene precursors for future reactions, thereby expanding the utilization of radical-type carbene transfer catalysis for the direct functionalization of C-H bonds and olefins.