A new redox initiator pair employing sodium sulfite as reducing agent was proposed to perform aqueous ambient RAFT/MADIX polymerization of N-vinylpyrrolidone (NVP) in the presence of a xanthate chain transfer agent. An efficient control of the polymerization with no formation of monomer byproducts was obtained regardless of the concentration of water in the medium. This system was applied to the aqueous synthesis of PVP-based double hydrophilic block copolymers through the polymerization of NVP at room temperature with several hydrophilic macro-chain-transfer agents based on poly(acrylamide), poly(acrylic acid), poly(sodium 2-acrylamido-2-methylpropanesulfonate), and poly(3-acrylamidopropyltrimethylammonium chloride). The diblock nature of the copolymers was established by DOSY NMR in all cases when satisfactory SEC analysis conditions could not be established due to the strong adsorption properties of the copolymers.