A vehicular exterior rearview mirror assembly includes a mirror head movably attached at a mounting base configured for mounting at a side of a vehicle. The mirror head includes a mirror casing and a mirror reflective element. An actuator is operable to move the mirror head relative to the mounting base between at least an extended position and a folded position. The actuator includes a first detent interface that is engaged to maintain the mirror head at the folded or extended position when the mirror head is moved via the actuator to that position. The actuator includes a second detent interface that is engaged to maintain the mirror head at the folded or extended position when the mirror head is manually moved to that position. The second detent interface is not engaged while the actuator moves the mirror head between the folded position and the extended position.