The union was founded in 1918 as the Society of Civil Servants (SCS), to represent intermediate class clerks.

[2] The Association of Executive Officers merged into the Society of Public Servants in 1930.

The merger left the union with 7,500 members, and this grew rapidly, to 24,000 by the end of World War II, and 46,000 in 1963, at which time more than 90% of eligible workers were members.

[3] The union merged with the Customs and Excise Group and Association of Officers of the Ministry of Labour in 1975, and the following year, it adopted its final name.

[3] By this period, in addition to the civil service, it had members in the Post Office and the UK Atomic Energy Authority.