We employ the Light–Induced Self–Writing (LISW) technique to fabricate vertically–aligned polymer composite microstructures with core–shell morphology. Nanoparticle (NP) organization occurs simultaneously with the structure growth, to form a distinct NP-rich ‘shell’ layer, and ‘core’ polymer solid. Photopolymerization–driven NP phase–separation was confirmed using in–situ Raman spectroscopy as well as ex–situ morphology analysis with EDS mapping. The microstructure array obtained consists of uniformly spaced, ∼250 μm tall ‘pillars’ that possess exemplary core–shell morphologies. Our results indicate that LISW is a highly attractive materials fabrication technique towards the development of polymer composite structures.