A hybrid catalyst system (CuBr/PS8-dMbpy)/(CuBr2/Me6TREN) for atom transfer radical polymerization (ATRP) was successfully used for preparation of polymers with complex polymeric architectures including star, graft, and bottle-brush copolymers. No significant differences between hybrid and CuBr/dNbpy homogeneous catalyst system were observed in the synthesis of 3-arm star poly(methyl acrylate) and poly(methyl methacrylate) graft copolymer with poly(lactic acid)/poly(dimethylsiloxane) mixed side chains. However, when PIB graft copolymers with styrene and methyl methacrylate were attempted by a "grafting-from" technique, a radical coupling resulted in a gel, due to a high local concentration of radicals with the hybrid catalyst system. This poor control was partially ascribed to poor solubility of the macroinitiator in the reaction medium, since the synthesis of molecular brushes was successful and the hybrid catalyst system afforded a well-defined poly(2-(2-bromopropionyloxy) ethyl methacrylate)-graft-poly(n-butyl acrylate) (pBPEM-graft-pnBA) from pBPEM as a macroinitiator. The polymerization in the presence of the hybrid catalyst system led to a faster reaction than that using a homogeneous catalyst system, while retaining a well-controlled reaction and affording polymers with narrow molecular weight distribution.