Graft copolymers have been prepared by one-step organometallic-mediated radical polymerization (OMRP) for the first time. Poly(ethylene glycol) acrylate (PEGA) was copolymerized with vinyl acetate (VAc) to yield well-defined P(PEGA-grad-VAc) gradient graft copolymers using bis(acetylacetonato)cobalt(II) as the control agent. The influence of experimental parameters such as the PEGA/VAc molar ratio, the nature of the initiator, and the temperature on the control of the copolymerization was discussed. The use of an excess of cobalt complex appeared as a key parameter to maintain a good level of control when higher contents of acrylate were used in the comonomer feed. The reactivity ratios were estimated and revealed that PEGA was added around 30 times faster than VAc, which gave access to a gradient P(PEGA-grad-VAc) copolymer or to a P(PEGA-grad-VAc)-b-PVAc diblock copolymer when the VAc polymerization was pursued after the full consumption of PEGA. The amphiphilic character of the copolymers makes them prone to self-assemble into micelles in water, as evidenced by dynamic light scattering.