Grand Manan measures 34 km (16 miles) long and has a maximum width of 18 km (11 miles) with an area of 137 km² (53 miles²). The closest point of mainland North America to Grand Manan is in Washington County, Maine, near the town of Lubec - the easternmost point of the continental United States, where the distance to the island measures 15 km (9 miles) across the Grand Manan Channel.
White Head Island, Gull Rock, Machias Seal Island and North Rock are part of the larger Grand Manan archipelago; the latter two are approximately 15 kilometres southwest of Grand Manan Island. Both Machias Seal Island and North Rock are claimed by both Canada and the United States. For administrative purposes, they form the most southerly part of New Brunswick. Machias Seal Island also houses the province's last remaining staffed lighthouse. The light has been in continuous operation since 1832; the post of lighthousekeeper was withdrawn for cost-saving reasons in the 1990s, but soon reinstated to provide a human demonstration of national sovereignty. The Canadian Wildlife Service also operates the bird sanctuary here, home to many puffins and terns during the breeding months. Research is conducted on the island by the Atlantic Cooperative Wildlife Ecology Research Network at the University of New Brunswick in Fredericton.
Used exclusively by the Passamaquoddy nation prior to European discovery, the island was first settled by Europeans in the late 18th century with the arrival of Loyalist refugees from the American Revolutionary War. Nonetheless the island's population maintained close economic ties with the United States, and smuggling was common in the early years of the nineteenth century. Grand Manan was initially included as part of the British colony of Nova Scotia until it was included in the new colony of New Brunswick, created in 1784. Grand Manan was also claimed by the United States until 1817 when this claim was dropped in exchange for Britain dropping its sovereignty claims over Moose, Frederick and Dudley islands in nearby Cobscook Bay.
The harbour at North Head is the primary destination for visiting pleasure boaters, though services are limited. Waters around Grand Manan are considered potentially dangerous due to terrain and weather. (Grand Manan was the site of many shipwrecks during the years when commercial steam and sail vessel traffic was high. There is a good display on this at the Maritime Museum in Halifax. The Grand Manan Museum houses one of the largest collections of shipwreck-recovered items in the Maritime provinces -- all gathered from the waters surrounding the island. Visitors can request access to a large collection of documents, books and journals dealing with all aspects of Grand Manan history and life.