Conductive nanowires were deposited by a focused gallium ion beam using W(CO)6 and (CH3)3CH3C5H4Pt as precursors. An in situ electrical treatment can substantially modify the structure and resistivity of these nanowires. This treatment consists in applying voltage ramps to the wire, leading to a high current density that induces wire annealing. The nanowires are deposited by focused ion-beam-induced deposition on two kinds of customized supports based on diamondlike carbon or Si3N4 membranes, particularly suitable for electrical tests and transmission electron microscopy characterization. In the case of tungsten wires, the treatment induces an improvement of the resistivity due to both gallium contamination removal and wire crystallization, which occurs at high temperature. The treatment leads to low-resistivity (50μΩcm) polycrystalline tungsten nanowires. For platinum wires, the treatment induces an increase of resistivity. In fact, this treated wire was composed of conductive droplets (platinum and PtGa2) connected by a wire with poor conductivity.