A highly active and chemoselective ionic organocatalyst is developed for room-temperature living/controlled ring-opening polymerization of lactide. The catalysts are prepared by a simple dehydration reaction between tetra-n-butyl ammonium hydroxide and an N,N'-diarylurea and used in cooperation with hydroxy initiators. Typically, poly(l-lactide) with near perfect isotacticity and widely tunable molar mass (4-130 kg mol-1) can be produced in <2 min (turnover frequency up to 120 000 h-1). Low molar mass distribution is observed in both short and substantially extended reaction times, clearly demonstrating the selectivity of catalyst for monomer enchainment over macromolecular transesterification. Versatile design and construction of diverse polylactide-based macromolecular structures are allowed thanks to the livingness of the polymerization and independence of initiator and catalyst. In addition to the hydrogen bond donor-acceptor type bifunctional activation mechanism, direct nucleophilic attack of the urea anion on the monomer and polymer is also shown which can be suppressed by the added hydroxy initiator.