Direct, nonvolatile, and reversible control of nanomagnetism in solid-state ferromagnetic thin films is achieved by controlling the chemical composition of the film through field-driven ion redistribution. The electric field-driven de-intercalation/intercalation of lithium ions can result in approximate to 100% modulation of the magnetization and drives domain wall motion over approximate to 100 nm. High-speed and multilevel magnetic information storage is further demonstrated.