Designer virus-inspired proteins drive the manufacturing of more effective and safer gene-delivery systems as well as simpler models to study viral assembly. However, the self-assembly of engineered viromimetic proteins on specific nucleic acid templates, a distinctive viral property, has proved difficult. Inspired by viral packaging signals, we harness the programmability of CRISPR-Cas12a to direct the nucleation and growth of a self-assembling synthetic polypeptide into virus-like particles (VLP) on specific DNA molecules. Positioning up to ten nuclease-dead Cas12a (dCas12a) proteins along a 48.5 kbp DNA template triggers particle growth and full DNA encapsidation at limiting polypeptide concentrations. Particle growth rate was further increased when dCas12a was dimerized with a polymerization silk-like domain. Such improved self-assembly efficiency allows for discrimination between cognate versus non-cognate DNA templates by the synthetic polypeptide. Our CRISPR-guided VLPs could help develop programmable bio-inspired nanomaterials with applications in biotechnology as well as viromimetic scaffolds to improve our understanding of viral self-assembly.