A device for unlocking a seat for a vehicle includes a base frame mounted on a movable rail of a seat rail, a seat frame mounted on the base frame to be able to tilt, a lock pin fixed to a side of the seat frame, a support bracket mounted on a floor panel, and a lock plate rotatably mounted on a side of the base frame, and configured to be locked to the lock pin when coming in contact with the support bracket and to be unlocked from the lock pin when coming apart from the support bracket, whereby it is possible to automatically unlock a seat when it is required to tilt the seat through a walk-in mechanism to secure a passage for a passenger to get in/out of a vehicle.