Grayson, the 24-year-old nephew of former All Blacks coach John Hart who has an Australian grandparent, replaces South African Sarel Pretorius as part of a revamped NSW backline.
Versatile Adam Ashley-Cooper moves from inside centre to fullback, with fellow Wallaby Lachie Turner returning from injury to replace Tom Kingston on the wing.
There are also two changes to the pack that started the Waratahs' last match against the Hurricanes.
Dean Mumm replaces Sitaleki Timani in the second row and Chris Alcock comes in for Jono Jenkins at openside flanker.
The Waratahs have lost their past six matches and are out of finals contention.