In solution-based synthesis of colloidal nanostructures, additions of ligands, stabilizers, and redox reagents are generally required to obtain desirable structures, though ligands and stabilizers on the surface of nanostructures can substantially affect the surface-related activity. Accordingly, an extensive rinsing process is usually required to remove residual reagents and stabilizers. This study reports a spontaneous self-biomineralization of palladium (Pd) ions on a filamentous virus to form ligand-free Pd nanowires under ambient conditions. No reducing reagents or additional surface stabilizers are used; the genetically modified virus alone supports the polycrystalline Pd nanowires within the nanostructure, maintaining the clean surface even without a rinsing process. The advantage of the ligand-free Pd nanowires is found in the Suzuki-coupling reaction, in which the nanowire catalytic activity is maintained after repeated reactions, while conventional Pd colloids undergo surface contamination by the stabilizer and lose their catalytic activity during repeated uses. The ligand-free surface, high electronic connectivity, and structural stability of the Pd nanowires also allow high sensitivity and selectivity in hydrogen gas sensing analysis. This work emphasizes the importance of the ligand-free surface of biotemplated nanostructures in maintaining functionalities without surface contamination.