A Deputy Mayor is a member of the London Mayoral cabinet, in the executive arm of the Greater London Authority. They serve as political advisors with responsibilities and powers corresponding to portfolios delegated by the Mayor. One of them must be designated as the Statutory Deputy Mayor, a member of the London Assembly who serves as the temporary Mayor during a vacancy or temporary incapacity of the Mayor.

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.