The timber trade, which specialized at first in spars for sailing ships, thrived on the wars of the early 19th century—the Napoleonic Wars and the War of 1812—when other British timber supplies were cut off. A shipbuilding industry grew up along the coast, particularly in Saint John. After conflicts over timber and river rights led to the Aroostook War—a near-clash between the militia of New Brunswick and Maine—a boundary was agreed upon in 1842.

In 1854 the Reciprocity Treaty with the United States introduced 11 years of duty-free trade in natural products. During this prosperous period, manufacturing began. However, the province still lacked railway connections with neighboring provinces.

In 1864 New Brunswick sent delegates to Charlottetown on Prince Edward Island to discuss some form of union with the other Maritime Provinces. It was thought that a union of the provinces could provide the resources to build an intercolonial railway. The Charlottetown delegates returned with resolutions to link not only the Maritime Provinces but also Ontario and Quebec. Despite some local opposition—for a time it appeared that New Brunswick would not join the confederation—New Brunswick became one of the four original members of the Dominion of Canada in 1867.

The coming of the railways in the latter 19th century drew New Brunswick into the mainstream of the Canadian economy. Moncton grew into a major transportation center. Saint John became a leading winter port for overseas shipment of Canadian products. With the passing of the wooden ship and development of the agricultural and industrial resources of the central and western provinces, however, New Brunswick suffered a gradual economic decline.

In the mid-20th century the Maritime Provinces, including New Brunswick, became popular with tourists from both Canada and the United States. During the 1970's New Brunswick's pulp and paper industry expanded, and deposits of antimony, a commercially important metal, were discovered in the province.

In the early 1980's the Miramichi River was dredged for use by oceangoing vessels. In 1984, and 1985, large potash deposits began being mined in southern New Brunswick. In 1987, New Brunswick elected its first Liberal government after nearly 20 years of Conservative rule. The Liberals remained in power after the 1991 elections.

In 1997, a bridge called Confederation Bridge opened. It stretches across the Northumberland Strait and connects New Brunswick with Prince Edward Island.

Also, in 1997, flooding occurred in the larger of the two potash mines, and it had to be closed as a result. In recent years, as the labor force has grown, an increasing number of people have been having trouble finding employment in New Brunswick.