A seat position adjustment apparatus for a vehicle may include fixed rails fixed on a bottom plane; first sliding rails configured to slide in forward and backward directions on the fixed rails respectively, and provided with cushion links rotatably coupled to the cushion frame; second sliding rails configured to move with the first sliding rails and slide on and protrude from the first sliding rails, and formed to support the cushion frame with the cushion links; a driving device mounted to the first sliding rails or the second sliding rails and configured to transmit power to the first sliding rails and the second sliding rails; and a seat back link rotatably mounted on the bottom plane or the fixed rails and rotatably coupled to and supporting a seat back frame.