Midfielder Smith has been released by Scunthorpe, despite a number of impressive displays in the youth and reserve teams.
And the 19-year-old has joined the Villagers, where he will play alongside former Iron winger John Eyre.
Ferriby manager Ryan France said: "Rob was recommended to me by (Scunthorpe assistant) Russ Wilcox and we stepped in as soon as he became available."