The mayor of London is the chief executive of the Greater London Authority. The role was created in 2000 after the Greater London devolution referendum in 1998, and was the first directly elected mayor in the United Kingdom.

The Greater London Authority (GLA), colloquially known by the metonym City Hall, is the devolved regional governance body of Greater London, England. It consists of two political branches: an executive Mayor and the 25-member London Assembly, which serves as a means of checks and balances on the Mayor. Since May 2016, both branches have been under the control of the London Labour Party. The authority was established in 2000, following a local referendum, and derives most of its powers from the Greater London Authority Act 1999 and the Greater London Authority Act 2007.