A photoinduced atom transfer radical polymerization (ATRP) of methacrylate with a Fe-based catalytic system was studied in the absence of additional ligands, reducing agents, and radical initiators. Linear semi-logarithmic polymerization kinetics and narrow molecular weight distributions were obtained in the presence but also absence of conventional ATRP initiators. The proposed mechanism involves monomer-mediated photoreduction of Fe(III) to Fe(II) but also photoactivation of Fe(II) species. The polymerization was studied with different radiation sources for several methacrylates. The technique was successfully used to synthesize block copolymers, confirming the living nature of ATRP.