Construction of core-shell nanostructures with ultrathin shells is a powerful way to leverage the lattice strain effect to enhance surface activity for a given catalytic reaction. Herein, we report a gold-catalyzed approach for growing a large variety of subnanometer-thick metal shells of up to several atomic layers on the gold cores. This strategy relies on a gold-catalyzed reduction of various metal precursors, in both aqueous and organic solvents, in which the metal atoms nucleate on the gold seed surfaces instead of self-nucleating in the solution. In addition, by coupling this gold catalysis with the galvanic replacement reaction, the ultrathin shell composition could be tuned to further optimize the lattice strain effect in the shell layer. This provides an effective way to equip the core-shell nanostructures with the desired catalytic performance in some key electrochemical reactions, for example, the ethanol oxidation reaction and oxygen reduction reaction. • Gold-catalyzed reduction of a variety of noble/transition metal ions is demonstrated • Gold catalysis can be used to make core-shell structures with subnanometer shells • Optimized core-shell nanostructures catalyze ethanol oxidation and oxygen reduction Core-shell nanostructures are promising composites for tunable catalysis. Here, Zeng et al. use gold-catalyzed reduction of noble and transition metal ions to direct the synthesis of core-shell nanostructures with a gold core and subnanometer shells for use in electrocatalysis.