Electrochromic glass has been used in many applications, such as the building envelope, because its light filtration can be adjusted in a controllable manner using low input energy. Electrochromic glass is a composite glass that consists of five layers. These five layers have two layers of glass, two layers of Indium Tin Oxide (ITO) and a layer of Poly (3-hexylthiophene), which is an electrochromic film. When a current passes through the glass, a voltage difference occurs, resulting in a redox reaction at an electrode layer. This causes the glass to change colour from transparent to opaque, resulting in a change in radiation absorption, which affects the heat transfer process. The study investigates temperature and thermal stress distributions in electrochromic glass by adjusting an input voltage in a range of 0–2.6 V. The spectral absorbance data at all light spectrum ranges were experimentally obtained. The averaged absorbance data were used for calculating the heat generation rate, and used as the input parameter for three-dimensional (3D) multiphysics simulations. The maximum temperature and thermal stress of the electrochromic glass are reached at 1.8 V according to the high rate of heat generation. The peak value of stress occurs at the interface between ITO and electrochromic layers. This study provides information regarding the heat transfer process and the stress induced in the electrochromic glass which varies with the applied voltages and can be applied to glass industries and many other related fields.