Mr Ruck, 59, is currently in a critical but stable condition after suffering head and leg injuries.
The incident happened at 19:40 BST on Saturday on New Street, Kidwelly, Carmarthenshire.
A man from nearby Burry Port has been arrested on suspicion of causing serious injury by failing to stop at a road traffic collision, police said.
Mr Ruck is the author of four books and a columnist for local newspapers.
He had been walking when the incident happened and was taken to Swansea's Morriston Hospital for treatment.
Dyfed Powys Police has appealed for witnesses to the incident.
A 19-year-old man has been arrested over a suspected hit-and-run that left writer Julian Ruck seriously hurt.