A fold-and-dive seat assembly for a vehicle is disclosed. The fold-and-dive seat assembly includes a seat cushion dived downward toward a floor panel by means of a dive link, a seat back connected to the seat cushion by a connection link, and rotatably connected to the floor panel to be folded toward the seat cushion, a head rest provided on an upper end of the seat back, a sliding unit, connected to the head rest and the seat back, for moving the head rest in a back and forth direction in a sliding manner, and a slid driving member for operating the sliding unit in link with the dive link, upon folding and diving, to slide the head rest in a rearward direction.