New Brunswick is bounded on the north by Quebec's Gaspé Peninsula and by Chaleur Bay. Along the east coast, the Gulf of Saint Lawrence and Northumberland Strait form the boundaries. In the south-east corner of the province, the narrow Isthmus of Chignecto connects New Brunswick to the Nova Scotia peninsula. The south of the province is bounded by the Bay of Fundy, which has the highest tides in the world with a rise of 16 m. To the west, the province borders the American state of Maine.

New Brunswick differs from the other Maritime provinces physiographically, climatologically and ethnoculturally. Both Nova Scotia and Prince Edward Island are either wholly or nearly surrounded by water and oceanic effects therefore tend to define their climate, economy and culture. New Brunswick on the other hand, although having a significant seacoast, is sheltered from the Atlantic Ocean proper and has a large interior which is removed from oceanic influences. The climate therefore tends to be more continental in character rather than maritime. The settlement patterns and the economy of New Brunswick also is different from its Maritime neighbours, in that it is more based on the provinces river systems rather than on its seacoasts.