The exploration of facile, low-cost, and universal synthetic strategies for high-performance aqueous energy storage is extremely urgent. The electrochemical activation tactic is an emerging synthetic technique that can turn inert or weakly active substances into highly active materials for aqueous energy storage via in situ or ex situ electrochemical treatment, which is receiving increasing attention due to its advantages of facile operation, variable control, high efficiency, flexibility, and wide applicability. This review first discusses the definition and general implementing methods of the electrochemical activation tactic, as well as the fundamental activation mechanisms, and then summarizes its applications in various aqueous systems, including rechargeable batteries and electrochemical capacitors with different charge carriers. The remaining challenges, potential solutions, and further perspectives are discussed finally. It is believed that this review will provide a timely summary and new inspiration for cutting-edge research on advanced aqueous energy storage devices.