A novel approach for the synthesis of ultra-long (up to ∼45 μm) vertically aligned barium titanate (BaTiO3) nanowire (NW) arrays on an oxidized Ti substrate is developed. The fabrication method uses a two-step hydrothermal reaction that firstly, involves the growth of ultra-long aligned sodium titanate NW arrays and secondly, involves the transfer of these precursor sodium titanate NW arrays to BaTiO3 NW arrays while retaining the shape of the template nanowires. The ion-exchange during the second hydrothermal reaction in barium hydroxide solution results in the structural transformation from single-crystal sodium titanate NW arrays to BaTiO3 NW arrays. This synthesis approach is low-cost, scalable, and enables control over the morphology and aspect ratio of the resulting BaTiO3 NW arrays by tuning the hydrothermal reaction parameters. In addition to the synthesis methods reported here, the energy harvesting behavior of the BaTiO3 NW arrays is evaluated as a function of their aspect ratio and demonstrated to produce significant impact on the energy produced. The newly developed hydrothermal synthesis process for controlled growth of ultra-long, vertically aligned BaTiO3 NW arrays provides a promising method for their efficient utilization in nano-electromechanical system-based sensors, energy harvesters, and nano-scale electronic devices.