Electric-field-driven ion migration can significantly modulate the electric and magnetic properties of solids, creating novel functionalities useful for advanced electromagnetic devices. Earlier works have used vertically stacked structures for this purpose, in which the redox process results from ion migration driven by a vertical electric field through the interfaces. However, the existence of the interfaces between the dissimilar layers causes the oxidation and reduction processes to have high and asymmetric energy barriers, which means that a large electric field is required to control the devices. Here, we show that in a partially oxidized single GdO(x)wire using a lateral electric field configuration, low and symmetric energy barriers for the oxidation and reduction processes can be achieved. We provide evidence that the redox process is the result of the lateral motion of oxygen ions by directly visualizing the electric-field-driven real-time ionic motion using an optical microscope. An electric field as low as 10(5) V/m was able to drive oxygen ions at room temperature, allowing controllable modulation of the electrical resistance using a lateral electric field. A large negative magnetoresistance was also observed in the GdO(x)wire, and its magnitude was significantly enhanced up to 20% at 9 T through oxygen ion control. Our results suggest that the electrical and magnetic properties of single GdO(x)can be efficiently controlled through oxygen ion motion driven by a lateral electric field, which paves the way for fully functional electromagnetic devices such as artificial synapses.