The first seamen’s unions in Australia were formed in Melbourne (1872) and in Sydney (1874). In 1876 the Melbourne Seamen’s Union and the Sydney Seamen’s Union amalgamated and, by 1880, there were seamen’s unions in all the eastern and south-eastern colonies of Australia as well as in several ports in New Zealand. The Federated Seamen's Union of Australasia was registered in 1906 under the Commonwealth's industrial relations legislation and, in 1907, Head Office was transferred from Melbourne to Sydney. Although the Federated Seamen's Union of Australasia was deregistered in 1925, in 1930 many of its members went on to form the Seamen's Union of Australasia which, in 1943, became the Seamen’s Union of Australia. Despite amalgamations with the Marine Cooks, Bakers and Butchers' Association of Australia in 1983, the Federated Marine Stewards and Pantrymen’s Association of Australasia in 1988 and the Professional Divers' Association in 1991, it remained the Seamen's Union of Australia until 1993 when it amalgamated with the Waterside Workers' Federation to form the Maritime Union of Australia.

Formed in Sydney in 1901 as the Firemen and Deckhands’ Association of New South Wales, by 1950 the name was changed to the Firemen and Deckhands’ Union of New South Wales. Throughout its history the Firemen and Deckhands’ Union underwent a number of amalgamations with other unions covering the maritime industry, including the incorporation of members of the Ferry and Tugboat Employees' Union (circa 1913) and the Marine Motor Drivers and Coxswains' Union in 1967. Gradually the Firemen and Deckhands' Union of New South Wales was absorbed into the New South Wales Branch of the Seamen's Union of Australia, beginning in 1976 with the establishment of a single national tugboat award and ending, in 1993, when the Seamen's Union of Australia amalgamated with the Waterside Workers Federation of Australia to form the Maritime Union of Australia.

Originally formed in 1912 as the Marine Motor Drivers’ and Coxswains’ Association of New South Wales, by 1939 the name had changed to the Marine Motor Drivers’ and Coxswains’ Union of New South Wales. Agitating for improvements in its members' pay and conditions and generally working towards maintaining the high standard of skill amongst workers in the industry, the Marine Motor Drivers’ and Coxswains' Union endured many demarcation disputes with other maritime unions such as the Masters’ and Engineers' Association and the Firemen and Deckhands' Union of New South Wales. In 1967, the Marine Motor Drivers’ and Coxswains' Union amalgamated with the Firemen and Deckhands' Union. Don Henderson, Secretary, Firemen and Deckhands' Union (FDU) (1962-1984), would later acknowledge that a large part of the FDU's motivation in seeking amalgamation with the Marine Motor Drivers and Coxswains was the vital position of the linesmen, represented by the latter union, in port operations. The linesmen's role in securing moored ships meant they could halt all docking of ships in the event of an industrial dispute.

The Dredge Employees' Union of New South Wales was formed in 1908. In September 1920 the name was changed to the New South Wales Dredge and Navigation Employees' Association. In February 1936, on the establishment of the Maritime Services Board, the union again changed its name to include Maritime Services Board employees. In 1971 the New South Wales Dredge and Maritime Services Board Employees’ Association amalgamated with the Seamen’s Union of Australia, which then amalgamated with the Waterside Workers' Federation in 1993 to form the Maritime Union of Australia.