A modular fender assembly for a vehicle includes a fender body having first and second body portions defining respective portions of the exterior of the fender body. First and second joiner brackets are bonded onto inner ends of the first and second body portions respectively. The joiner brackets have joiner flanges which can be joined with one another in parallel abutment to join the first and second body portions. Either body portion of the fender can thus be trimmed to length to suit the application prior to bonding the joiner bracket in position according to the new trimmed length. The joiner brackets typically have multiple overlapping and interlocking joiner flanges which span across the abutted seam between the two adjacent fender body portions, including upright stiffener flanges, for improving strength to reduce bending and sagging of the fender assembly at the seam.