Na2Ti6O13 nanoplates, nanowires, and continuous nanowire network films are hydrothermally formed on a large scale directly on Ti substrates for the first time. The morphology of the formed Na2Ti6O13 nanostructures can be easily tuned by varying the experimental parameters of temperature, reaction duration, and the NaOH concentration. Our study demonstrates that the synthesized Na2Ti6O13 nanostructures are easily converted into H2Ti3O7 nanostructures—a desirable precursor for the fabrication of various TiO2-based nanomaterials—with shape preservation, by an ion-exchange process. Anatase, a mixture of anatase and rutile, and rutile TiO2 nanowires are formed when the H2Ti3O7 nanowires are annealed at 450, 600, and 750 °C, respectively. The optical properties and the photocatalytic activity of H2Ti3O7 nanowires and of the TiO2-based nanomaterials are also addressed. The approach described in this study provides a simple and novel method for the large-scale synthesis of various TiO2-based nanostructured materials that grow directly on Ti substrates and are ready for a wide range of practical applications, such as the photodegradation of wastewater.