By 1890, a number of these unions had come together to form a loose federation called the Federated Seamen's Union of Australasia, which included New Zealand until Australia became a nation in 1901, and was called the Seamen's Union of Australia (SUA) from 1906 onwards. For nearly eighty years the SUA successfully improved the wages and conditions of its members by negotiations with employers and governments or by taking militant industrial action.
In the period following the First World War the Seamen's Union gained a reputation as a militant union, under the leadership of socialist-inclined Tom Walsh. During the Second World War it was instrumental in ensuring the supply of civilian seafarers for the war effort.
The SUA also took part in a wide range of social and political issues over the years, for example campaigning for Aboriginal rights, opposing apartheid in South Africa, and opposing the Vietnam War. The union's longest serving leader was Eliot V. Elliott who led the SUA from 1941-1978. In 1993 the SUA amalgamated with the Waterside Workers' Federation (founded in 1902) to form the Maritime Union of Australia.