An exterior rearview mirror assembly for mounting at a vehicle includes a mounting arm configured for attachment at an exterior portion of the vehicle, and a mirror head having a mirror casing, a mirror reflective element and a mirror actuator. The mounting arm is received through an aperture in the mirror casing and the mirror actuator is attached at the mounting arm inside the mirror casing. The mirror actuator is electrically operable to adjust the mirror reflective element and the mirror casing relative to the mounting arm. The aperture allows for movement of the mirror casing relative to the mounting arm during operation of the mirror actuator. A powerfold actuator may be operable to pivot the mirror head relative to the base portion between a folded or non-use position and an extended or use position.