A vehicular exterior rearview mirror system includes a vehicle door having an inner sheet metal portion and an outer sheet metal portion. A base bracket includes (i) a body portion, (ii) a mirror mounting portion that extends from the body portion and (iii) an attaching portion that extends from the body portion. The attaching portion is attached at the inner sheet metal portion of the vehicle door. The body portion of the base bracket is partially disposed at an interior portion of the vehicle door between the inner sheet metal portion and the outer sheet metal portion. The mirror mounting portion extends outboard of the outer sheet metal portion from the body portion. A mirror head is attached at the mirror mounting portion of the base bracket. The mirror head includes a mirror reflective element.