The breed originated in Newfoundland from dogs indigenous to the island. There is some speculation they may be partly descended from the big black bear dogs introduced by the Vikings in 1001 A.D.[3] However it is more likely that their size results from the introduction of large mastiffs, brought to the island by generations of Portuguese fishermen. By the time colonization was permitted in 1610, the distinct physical characteristics and mental attributes had been established in the breed for all time.

In the early 1880s fishermen from Ireland and England traveled to the Grand Banks of Newfoundland where there were two main types of working dog: one more heavily built, large with a longish coat, whereas the other was lighter in build, an active, smooth-coated water dog. The heavier one was the Newfoundland and the other was the St. John's Dog, the forerunner of the Labrador Retriever. The dogs were used in similar ways to pull fishnets and heavy equipment.