The Montrealer was an overnight passenger train between Washington, D.C., United States, and Montreal, Quebec, Canada. The train was operated from 1924 to 1966, and again under Amtrak from 1972 to 1995, excepting two years in the 1980s. The train was discontinued in 1995 and replaced by the Vermonter, which provides daytime service as far north as St. Albans, Vermont. Current Amtrak service to Montreal is provided by the daytime Adirondack from New York City via Albany.

The original Montrealer entered service on June 15, 1924. The train provided overnight service from Washington, D.C., to New York City and Montreal on a route that passed through New England. The Washingtonian operated over the same route in the southbound direction.

Both trains ran over five railroads: the Pennsylvania Railroad, the New Haven Railroad, the Boston & Maine Railroad, the Central Vermont Railway, and the Canadian National Railway, which worked together to provide the equipment and crews to operate the train.

When it was inaugurated, the Montrealer also provided through service to Ottawa and Quebec City. During the summer months the Quebec car originated a few days a week in Murray Bay, a resort area 86 miles (138 km) northeast of Quebec City.

North of the U.S.-Canadian border, in early years the train traveled east of Missisquoi Bay and through Iberville on the route north to Montreal. By the 1950s the route was rerouted through Alburg, Vermont, and in Quebec made stops at Cantic, St. Johns and St. Lambert before reaching Montreal.

The Montrealer and the Washingtonian first ran during the days of Prohibition in the United States. The Washingtonian became known unofficially as "The Bootlegger" or simply "The Boot" because passengers often carried well-hidden bottles of liquor on the southbound train. During the Prohibition years the Washingtonian was a favorite target of U.S. federal agents who would board in St. Albans and search the train looking for illegal liquor. During the 1940s extra sections of the train were added for skiers on weekends in the winter months from New York to Waterbury, Vermont.

By the 1960s, service consisted of two daily round trips: the Washington–Montreal Montrealer/Washingtonian, and the New York City–Montrealer section of the Ambassador. On September 6, 1966, the trains were unceremoniously discontinued between Montreal and Springfield, Massachusetts. Previously, the Ambassador had been an entirely separate day train counterpart to the Montrealer. The New Haven Railroad continued to operate its portion of the train between Springfield and New York City until December 31, 1968, when most passenger service on the New Haven–Springfield Line was discontinued, upon the implementation of the merger of the New Haven Railroad into the Penn Central.

In 1972, Congress passed a spending provision that required Amtrak to restore service to Canada, specifying the new route had to connect Montreal to Washington, DC. The law set off a competition between officials in New York State and Vermont as both vied to host the new route. New York officials cited better track conditions on the Delaware & Hudson Railroad route and that fact that it was 59 miles shorter. It also required less expensive infrastructure work to host passenger trains, just $1.6 million compared to $3.4 million in Vermont. However, Vermont won out as the train would have been able to serve Pennsylvania Station and points south such as Philadelphia and Washington. The New York route would have required a transfer from Grand Central Terminal. New York state funded its own Adirondack service in 1974, its day-time service complimenting the Montrealer’s overnight schedule.