A simple and efficient route to gold-polymer nanoparticle composites is described. Our versatile synthetic route exerts facile control over polymer nanoparticle morphology, including micelles, rod-like structures, and vesicles, all easily attainable from a single polymerization taken to different monomer conversions. Specifically, poly[oligo(ethylene glycol) methacrylate]-b- poly(dimethylaminoethyl methacrylate)-b-poly(styrene) (POEGMA-b-PDMAEMA-b-PST) triblock copolymers were synthesized using a polymerization induced self-assembly (PISA) approach. Subsequently, spherical gold nanoparticles (10 nm AuNPs) were formed at the hydrophilic-hydrophobic nexus of the assembled triblock copolymer nanoaggregates by the addition of chloroauric acid (HAuCl4) followed by in situ reduction using NaBH4. After reduction, the cloudy white nanoparticle dispersions turned to a red-purple color. The gold nanoparticles that formed were stabilized by the enveloping polymeric nanostructures, neither precipitation nor agglomeration occurred. We demonstrated that we were able to tune the gold nanoparticle composition in these polymer-gold composites by varying the concentration of chloroauric acid. Morphology, particle size, molecular weight, AuNP content, and chemical structure of the polymer structures were characterized by transmittance electron microscopy (TEM), dynamic light scattering (DLS), size exclusion chromatography (SEC), thermal gravimetric analysis (TGA), and 1H NMR. Finally, the formation of the AuNPs occurred without affecting the polymer nanoparticle morphology.