We describe the calibration and performance of the Mars Odyssey spacecraft's Thermal Emission Imaging System visible imaging subsystem (THEMIS VIS) and present comparisons with other instruments in order to validate the results. The main challenge to the THEMIS VIS calibration process is the significant amount of stray light that accumulates during both integration and readout. The stray light is influenced by scene elements outside of the field of view of the THEMIS VIS detector, and so its magnitude can only be estimated. As a result, residual stray light artifacts are common in calibrated THEMIS VIS images and are especially prominent when the exposure time is short, or the scene contrast is high. Nevertheless, our absolute 2σ calibration uncertainty for the central region of the most frequently used THEMIS VIS channel, the 654 nm band, is better than 5% for all but the shortest exposures times, and our comparisons with Hubble Space Telescope and Mars Exploration Rover measurements show no evidence of systematic calibration inaccuracies.