Transcranial direct current stimulation (tDCS) is a noninvasive and portable brain stimulation technique that is ideally suited to augment human brain performance in everyday settings. The aim of this study was to measure and model the time course of bilateral cortical hemodynamics (using functional near-infrared spectroscopy, fNIRS) and neural activity (using electroencephalography, EEG) during tDCS. Subjects received real (tDCS-1 and tDCS-2) and sham anodal tDCS (2 mA) targeting the left sensorimotor cortex (SMC) via a 4 × 1 high-definition electrode montage. Simultaneous EEG (23 channels) and fNIRS (16 channels) were used to measure changes in left and right SMC activity (EEG: frequency) and hemodynamics (fNIRS: oxyhemoglobin concentrations, O2Hb) during the stimulation. The O2Hb time course showed a greater increase in the fNIRS channels surrounding the anode in the stimulated left SMC during the real tDCS sessions compared to the sham. In a subsample of five subjects, a Kalman filter using an autoregressive exogenous model was able to appropriately track O2Hb signals using EEG band-power signals. The neuronal (EEG) and hemodynamic (fNIRS) responses in the stimulated left SMC region can lend to closed-loop control of anodal tDCS for optimized neuromodulation in various neuroergonomic applications.