A new synthetic strategy for the preparation of colloidal clusters of core-shell nanoparticles with plasmonic cores and catalytically active shells is reported. The Au@M (M = Pd or Pt) nanoparticle clusters (NPCs) with a high density of sub-1 nm interparticle gaps were successfully prepared by the deposition of Pd or Pt shells onto thermally activated Au NPCs. The prepared Au@M NPCs showed remarkably enhanced plasmonic performance compared to their Au@M nanoparticle counterparts, which can be attributed the localization of a strong electromagnetic field at the interparticle gaps. In situ real-time Raman spectroscopy and plasmon-enhanced electrocatalysis experiments demonstrated that the controlled assembly of core-shell nanoparticles is a very effective route for the synergistic integration of plasmonic and catalytic functions in a single platform.