Janus particles have attracted significant attention in recent years, due to their potential in nanomanufacturing. Their asymmetric features impart unique physical and chemical properties, which can be tuned and utilized to control their solution-state assembly. While several examples of Janus nanostructures have been reported in the literature, the scientific community continues to pursue synthetic routes which are less time and resource intensive. Herein, we describe a facile method to synthesize Janus nanoparticles in which colloidal micelles template the in situ formation of Aunanoparticles in the shell layer. The resulting morphologies of the hybrid Au–polymernanoparticles can be adjusted widely by controlling the polymer and reducing agent (HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid)) concentrations. High-fidelity populations of Au–micelle Janus nanoparticles are obtained when the polymer concentration is high (≥1.0 × 10−6 mmol L−1) and the HEPES concentration is low (≤0.3 mol L−1). Conversely, when the HEPES concentration is high (≥0.5 mol L−1) and the polymer concentration is low (≤2.4 × 10−7 mmol L−1), raspberry-like clusters are formed, where each micelle encumbers several Aunanocrystals. Our method is attractive in that the number of Aunanoparticles on each Au–micelle entity can be controlled using a scalable, aqueous solution process. It also has significant potential for the directed assembly of Aunanoparticle superstructures, as the nature and geometry of the polymer precursors can be varied.