High-density thermodynamically stable nanostructured copper-based metallic systems, and methods of making, are presented herein. A ternary high-density thermodynamically stable nanostructured copper-based metallic system includes: a solvent of copper (Cu) metal; that comprises 50 to 95 atomic percent (at. %) of the metallic system; a first solute metal dispersed in the solvent that comprises 0.01 to 50 at. % of the metallic system; and a second solute metal dispersed in the solvent that comprises 0.01 to 50 at. % of the metallic system. The internal grain size of the solvent is suppressed to no more than 250 nm at 98% of the melting point temperature of the solvent and the solute metals remain uniformly dispersed in the solvent at that temperature. Processes for forming these metallic systems include: subjecting powder metals to a high-energy milling process, and consolidating the resultant powder metal subjected to the milling to form a bulk material.