jats:titleAbstract</jats:title>jats:pThe galvanic replacement reaction is a robust tool for the controlled synthesis of hollow and semihollow bimetallic nanostructures, which have applications in a range of science, engineering, and medical fields due to the tunability of their localized surface plasmon resonances (LSPRs) and surface chemistry. Here, a controllable galvanic replacement of Ag by Au coupled with coreduction is described, performed in nonaqueous solvents including methanol, ethanol, and an jats:italicN,N</jats:italic>‐dimethylformamide:toluene mixture and yielding hollow and semihollow alloyed nanoparticles. Structural control, from semihollow to nanoshell, and plasmon tunability are demonstrated via control of the Au:Ag stoichiometry. The high structural dependence on temperature is shown, with striking changes in nanoparticle surface smoothness and pinhole density, and reveals the optimal reaction temperature to be 65 °C in alcohols. Through optimizing this reaction, smooth closed shell AgAu alloy nanoparticles with LSPRs tunable from 494 to 567 nm are obtained. This work provides a framework for galvanic replacement of large anisotropic Ag nanoparticles with Au in nonaqueous media, which can be extended to other solvent systems suitable for air‐sensitive metals and precursors.</jats:p>