Herein, we reported an N-heterocyclic carbene (NHC) and photo-co-catalyzed alkylacylation of olefins in the presence of the versatile synthon diazo ester, providing a new idea for transient radical generation with the only byproduct being N2. Particularly, this radical process employs traditional carbene precursor diazo esters as the radical source, which is the first case in NHC catalysis. Compared to the previous pathway that produces radicals with large discard fragments, this merged channel possesses great atom economy.