Formed in 1910 and registered just a year later, the Fire Brigade Employees' Union of New South Wales was the first known trade union of firefighters in the world. By 1922 it had changed names to the Fire Brigades Association of New South Wales, but officers remained excluded. In 1948, the officers' and firefighters' associations formally amalgamated and were registered under the title of the New South Wales Fire Brigade Employees' Union. Officers joined firefighters on strike for the first time, over pay. Just a year later, in 1949, a splinter group of senior officers formed an independent Senior Officers' Association. By 1975, the Senior Officers' Association and the FBEU formally amalgamated. From 1990, the NSW Fire Brigade Employees' Union identified as the NSW Branch of the United Firefighters Union of Australia.

The New South Wales Fire Brigade Officers' Association was a separate organisation from the Fire Brigades Association of New South Wales representing a distinction between officers and firefighters. Its earliest minutes of meetings date from 1925. In 1948 it amalgamated with the Fire Brigades Association of New South Wales to form the New South Wales Fire Brigade Employees' Union. Officers joined firefighters on strike for the first time, over pay. Just a year later, in 1949, a splinter group of senior officers formed an independent Senior Officers' Association. By 1975, the Senior Officers' Association and the FBEU formally amalgamated.

In 1949, a splinter group of senior officers in the New South Wales Fire Brigade Employees' Union formed the independent New South Wales Fire Brigade Senior Officers' Association. This was just one year after the previous New South Wales Fire Brigade Officers' Association had amalgamated with the Fire Brigades Association of New South Wales to form the New South Wales Fire Brigade Employees' Union in 1948. By 1975, the Senior Officers' Association and the Fire Brigade Employees' Union formally amalgamated.