Well-controlled polymerization of methyl methacrylate at 35 °C was achieved by photochemically mediated atom transfer radical polymerization using a copper catalyst concentration as low as 50–100 ppm. Irradiation at λ > 350 nm provided both a reduction of initially added copper(II) catalyst complexed with either PMDETA or TPMA ligand to a copper(I) activator and a sufficient rate of polymerization. Poly(methyl methacrylate) with a narrow dispersity and predictable molar mass was obtained when an initiator, such as 2-bromopropionitrile, was used. Successful chain-extension polymerization confirmed the living character of the photopolymerization system.