A vehicular interior rearview mirror assembly includes a mirror head having a mirror casing and an electro-optic mirror reflective element. A printed circuit board is disposed in the mirror head and includes (i) a light sensor, (ii) an indicator LED and (iii) an electronic switch. A multi-function light pipe is disposed at the mirror head with (i) a first end at the light sensor, the indicator LED and the electronic switch, and (ii) a second end at a perimeter region of the mirror head so as to be viewable and accessible by the driver of the vehicle. The light sensor senses light from rearward of the vehicle via the light pipe. Light emitted by the indicator LED, when energized, is viewable by the driver via the light pipe. The light pipe actuates the electronic switch responsive to a user actuation at the second end of the light pipe.