Nanowire memristor devices that display multilevel memory effects are of great interest for high-density storage, however, numerous challenges remain in fabricating high-quality, stable memory units. A plasmonic-radiation-enhanced technique is introduced in this work for scalably forming nanowire multilevel memory units with superior properties. Femtosecond laser irradiation of gold-titanium dioxide nanowire-gold structures results in plasmonic-enhanced optical absorption in the TiO2 locally at the metal-oxide interface. This produces junctions with superior mechanical and electrical contact, and engineers a concentration of charged defects in the TiO2 near the interface, which enables stable multilevel memory behavior without the need for a traditional electroforming step. The memory units produced display eight-level current amplification under continuous forward voltage cycles, and can replicate complex multilevel memory sequences without interference between the different multilevel states.