SH 63 begins just to the east of Renwick at SH 6, and parallels the course of the Wairau River for 93 kilometres, originally to the south of the river before crossing to the north side about 20 km from the Marlborough/Tasman border, while passing through the settlements of Wairau Valley, Hillersden and Tophouse. Just before reaching Tophouse, the Wairau River veers to south while the road arrives in St. Arnaud at the shores of Lake Rotoiti. After St. Arnaud the road swings to the northwest and follows the last 24 km alongside the Buller River. At Kawatiri Junction, it terminates at SH 6 between Murchison and the Hope Saddle.