Self-assembly of plasmonic metal nanoparticles can provide an opportunity of creating colloidal superparticles with fascinating optical properties arising from interparticle plasmonic coupling, but typically requires multiple steps involving solvent and/or ligand exchange. We developed a direct, one-step chemical synthesis of plasmonic black colloidal Au superparticles with broadband absorption in visible and near-infrared regions. During the synthesis, the Au superparticles were formed through self-assembly of in-situ-formed Au nanoparticles driven by solvophobic interactions between nanoparticles and solvent. These superparticles could be solution-processed to fabricate a thin film, which exhibited near-perfect absorption over a broad range from 400 nm to 2.5 mu m as well as the excellent antireflective property. Thanks to their broadband absorption property, the Au superparticles showed good performances for near-infrared surface-enhanced Raman spectroscopy and light-to-heat conversion.