The Brotherhood of Railroad Trainmen was founded in 1883 in Oneonta, N.Y. as a protective and insurance organization. By the time of its merger with three other railroad labor unions to form the United Transportation Union in 1969, it had the greatest membership of any of the operating railroad brotherhoods.

The Brotherhood of Railroad Trainmen (BRT) was established to represent members' interests in obtaining a satisfactory contract with management. The first Canadian lodge was established in Moncton, New Brunswick in 1885, and the first Ladies' Auxiliary was organized in Fort Gratiot, Mich. in 1889. These records reflect the union's political and fraternal activities as well as its actions in the areas of collective bargaining, grievances, and railroad and labor legislation. As the largest of the unions which merged to form the United Transportation Union in 1969, the bulk of its then current files formed the basis for the files now held in the merged union's headquarters.

The rail service members of the BRT included conductors and their assistants, dining car stewards, ticket collectors, train baggagemen, brakemen, and train flagmen. The yard service members of the BRT included yardmasters, yard conductors, switchtenders, foremen, flagmen, brakemen, switchmen, car tenders, operators, hump riders, and car operators. In 1933, the BRT organized interstate bus operators, and included them under BRT contracts held with U.S. bus companies.

BRT officers were elected at the Grand Lodge Convention of the Brotherhood, held every 4 years. The principal officers included a president, an assistant to the president, a general secretary-treasurer, Canadian and national legislative representatives, a senior vice-president, BRT representative, and National Railroad Board of Adjustment representative. The BRT had four governing boards: the Board of Directors, Board of Trustees and Insurance, Board of Appeals, and Executive Board.