Highway 523 begins at the boundary between the Hastings County and Nipissing District, east of Algonquin Provincial Park. From here the road continues south as the Madawaska Road to Maynooth, where it meets the Peterson Road and Hastings Road, all former Colonization Roads which served to open the northern frontier to settlement in the 1850s. North of the boundary, the Highway begins and is known as Cross Lake Road. It passes through a sparsely populated region dotted with lakes and muskeg, generally remaining straight, though curving sporadically to avoid the many obstacles presented by the Canadian Shield.^[2]

After passing through the village of Cross Lake, situated on the eastern shore of a lake with the same name, the highway abruptly curves to the east for 1 kilometre (0.62 mi). It turns back to the north and later approaches the northwestern tip of Bark Lake, on the opposite shore as Bell Bay Provincial Park. Here the highway curves to the west and follows the delta of the Madawaska River, curving north just short of entering the village of Madawaska. It ends at an intersection with Highway 60.^[2]

Highway 523 was first designated along with many of the secondary highways in Ontario in 1956.^[3] The route was paved at the time of assumption,^[4] and has remained the same since.^[2]

The following table lists the major junctions along Highway 523, as noted by the Ministry of Transportation of Ontario.^[1] The entirety of the highway is located within Nipissing District.^[2]