A thermal defogging system and method for an optical instrument is described. In one embodiment, the thermal defogging system for an optical instrument is comprised of: at least a primary housing, the primary housing defining an aperture for transmission of optical signals, a transparent element adapted to be aligned with the aperture for transmission of optical signals, at least one side of the transparent element facing the external environment; and a transparent conductive layer covering an area at least as large as the optical footprint of the transmitted optical signal through the transparent element, wherein responsive to the application of electrical power to the transparent conductive layer, the transparent conductive layer generates heat that is thermally communicated to the least one side of the transparent element facing the external environment.