Elected county councils were established in 1889 under the Local Government Act 1888, taking over administrative functions previously carried out by unelected magistrates at the quarter sessions.

The council formally came into being on 1 April 1889, on which day it held its first official meeting at the Moot Hall, Newcastle upon Tyne, the courthouse (built 1811) which had served as the meeting place of the quarter sessions which preceded the county council.

[6] The first chairman of the council was Matthew White Ridley, who was also the Conservative MP for Blackpool (in Lancashire).

In 1974 the lower tier was reorganised and Northumberland was left with six districts: Alnwick, Berwick-upon-Tweed, Blyth Valley, Castle Morpeth, Tynedale and Wansbeck.

As part of the 2009 structural changes to local government in England, Northumberland's six districts were abolished and their functions were taken over by the county council.

[14] In 2024 a combined authority was established covering Northumberland, County Durham, Gateshead, Newcastle upon Tyne, North Tyneside, South Tyneside and Sunderland, called the North East Mayoral Combined Authority.

It is chaired by the directly elected Mayor of the North East and oversees the delivery of certain strategic functions across the area.

The whole county is also covered by civil parishes, which form an additional tier of local government.