St. Paul Island is a small uninhabited island located approximately 24 kilometres northeast of Cape North on Cape Breton Island and 71 kilomtres southwest of Cape Ray on Newfoundland; it is along the boundary between the Gulf of St. Lawrence and the Cabot Strait.

An extension of the Appalachian Mountains and the Cape Breton Highlands, the highest point on St. Paul Island is 147 metres (485 feet) upon "Croggan Mountain".

St. Paul Island is formed of granite and is extremely rugged with its shores being completely encircled by rockface cliffs. There are no land animals on the island, although it is inhabited by numerous seabirds. Its ecosystem is considered fragile and due to the danger posed by visiting the island, visits must be cleared with the Canadian Coast Guard (the island's owner) beforehand.

The island is nicknamed the "Graveyard of the Gulf" (of St. Lawrence) as it is fog-bound throughout much of the navigation season and posed a significant hazard during the age of sail.