A vehicular exterior rearview mirror assembly includes a mirror reflective element sub-assembly having a mirror reflective element, a mirror reflector, a mirror back plate, a heater pad and a blind spot indicator module. The heater pad is disposed between the mirror reflective element and the mirror back plate and has a light transmitting portion that is aligned with an aperture of the mirror back plate. The blind spot indicator module includes a body portion and a connector portion extending from the body portion. Light emitted by at least one light emitting diode of the blind spot indicator module passes through the light transmitting portion of the heater pad and through a light-transmitting portion of the mirror reflector and exits the mirror reflective element to provide a visual icon visible to a driver of the vehicle who is driving the vehicle and who is viewing said mirror reflective element.