Between Glen Innes and South Grafton, Gwydir Highway runs between the Gibraltar Range and Washpool National Parks.

12) from the intersection with North Coast Highway (today Pacific Highway) in South Grafton, via Buccarumbi, Glen Innes, Inverell, Moree to the crossing of the Barwon River at Mogil Mogil,[2] and Main Road No.

68 was declared along its future alignment from Walgett via Collarenabri to Mogil Mogil (and continuing northwards to the state border with Queensland, and westwards via Brewarrina, Bourke, Louth, Wilcannia, Menindee, Pooncarrie and Wentworth to the state border with South Australia)[2] on the same day, 8 August 1928.

Under this act, the western end of Gwydir Highway (as State Highway 12) was extended from Collarenabri to the intersection with Castlereagh Highway north of Walgett, subsuming the former alignment of Main Road 68 (formerly Trunk Road 68, officially splitting it into a western section terminating at Walgett, and an eastern section terminating in Collarenabri), on 17 December 1993.

With New South Wales' conversion to the newer alphanumeric system in 2013, this was replaced with route B76 across the whole highway.