Conventional vanadium chemistries have been hindered by limited capacity inherent to the ion-insertion mechanism and modest redox potentials in near-neutral media, constraining their suitability for high-energy aqueous batteries. Here we demonstrate a conversion-type vanadium redox that delivers concomitant superiority in capacity and potential for aqueous batteries. OH−-mediated chemical activation promotes V–O bond cleavage, thereby driving a transition from the single-electron insertion reaction to the four-electron conversion reaction. As confirmed by in situ synchrotron characterizations, a tailored mesoporous architecture enriches local OH−, facilitating the reversible conversion between V2O3 and Na3VO4. The conversion anode delivers a high specific capacity of 700 mAh g−1 with 98% vanadium utilization, a low redox potential of −0.95 V versus standard hydrogen electrode and reversible cycling over 3,000 cycles. An alkaline Ni–V battery is fabricated, with a projected whole-battery-level energy density of up to 110 Wh kg−1. This work paves the way to tuning the reaction pathway and offers insights into multielectron redox design for next-generation aqueous batteries.