A transfer seat base for a vehicle, including a rail frame having rails; a carriage frame positioned to ride along the rails and configured for receipt of a seat mounted thereto; a powered motive mechanism for, upon actuation, longitudinally moving the carriage frame along the rails between a forward driving position and a rearward occupant transfer position; a locking mechanism operable upon cessation of actuation of the motive mechanism to automatically lock the carriage frame against longitudinal movement at various positions between the forward driving position and rearward occupant transfer position.