The synthesis of ethylene-based block copolymers (BCPs) by using a single radical polymerization technique is attractive but remains to be a great challenge. The main difficulty relates to the difference in reactivity between ethylene and the comonomer, especially if polar vinyl monomers are considered. The present work explores the radical polymerization of ethylene via organometallic-mediated radical polymerization (OMRP) with the aim of overcoming this limitation. First, some organocobalt complexes demonstrated their ability to initiate the radical homopolymerization of ethylene. The molecular parameters of polyethylene (PE) were found to be dependent on the reaction conditions (solvent and temperature), but at this stage, data do not allow claiming the controlled character of this polymerization. Nonetheless, proper selection of the organocobalt complex initiator led to unique alpha-functional PE. Finally, BCPs composed of ethylene and polar vinyl monomers, for example, poly(vinyl acetate)-b-polyethylene (PVAc-b-PE) and poly(ethylene vinyl acetate)-b-polyethylene (EVA-b-PE), were prepared for the first time using cobalt-terminated polymers as macroinitiators. In this case, some triblock copolymers were also formed by radical coupling reactions during ethylene polymerization. Overall, this strategy is straightforward for preparing PE-based copolymers by using a single organocobalt complex.