AbstractAtom transfer radical polymerization is successfully conducted with an organic semiconductor (OS)‐based visible light activated photocatalyst via a precisely designed catalytic cycle. The living nature of the polymerization by the OS type photocatalyst is proved by the linearly‐increasing molecular weight with consumption of the monomer, the expected molecular weight from MALDI‐TOF measurements, and the chain extending reaction, as well as block copolymer synthesis. Benefitting from clear and measurable reductive potential as well as the oxidative potential of the OS‐type photocatalyst, the intrinsic demand for “living radical polymerization” is discussed and examined, which indicates the diversity and great potential of OS‐type photocatalysts for organic synthesis.