A tonneau cover system for a vehicle having a cargo box and a tailgate movable between an open position and a closed position. The tonneau cover system includes a tonneau cover mountable to the vehicle and movable between deployed and open arrangements. In the deployed arrangement, the tonneau cover overlies the cargo box. In the open arrangement, the tonneau cover is opened for allowing access to the cargo box. A latch mechanism is movable between a locked position in which the latch mechanism secures the tonneau cover in the deployed arrangement, and an unlocked position in which the latch mechanism is released to allow movement of the tonneau cover into the open arrangement. The latch mechanism is biased in the unlocked position and comprises a tailgate contact positionable to engage the tailgate in the closed position to move the latch mechanism from the unlocked position to the locked position.