Established in 1851, the original Amalgamated Engineering Union was a branch of the British union. It was registered with the Commonwealth Conciliation and Arbitration Court in 1905 and became known as the Amalgamated Society of Engineers. In 1920 it amalgamated with ten other engineering and allied trade unions and changed its name to the Amalgamated Engineering Union, Australian Section in 1921. In 1968 the union became autonomous from its parent body in Britain, shortening its name to the Amalgamated Engineering Union to reflect this. In mid-June 1972 the AEU began a series of amalgamations with the Sheet Metal Workers, Blacksmiths & Boilermakers and Federated Jewellers to form the Amalgamated Metal Workers' Union by 1973.

The Boilermakers and Blacksmiths Assistants' Society of South Australia existed from at least 1908. It amalgamated with the Cast Iron, Pipe Moulders' and Ironworkers' Society of Adelaide in 1914 as the South Australian Branch of the Federated Ironworkers' Association.

The Amalgamated Metal Workers Union originally formed in 1973 from the amalgamation of the Amalgamated Engineering Union, the Sheet Metal Working, Agricultural Implement and Stovemaking Industrial Union of Australia, the Boilermakers' and Blacksmiths' Society of Australia, and the Federated Jewellers. In 1976 the union amalgamated with the Federated Shipwrights' & Ship Constructors' Association of Australia to become the Amalgamated Metal Workers & Shipwrights Union. In 1983 it joined the Federated Moulders (Metals) Union of Australia to become the Amalgamated Metals Foundry and Shipwrights' Union. It reverted to the name Amalgamated Metal Workers' Union in 1985 and operated until 1991 when it amalgamated with the Association of Draughting Supervisory & Technical Employees to become the Metals & Engineering Workers' Union.