The Commonwealth Secretariat is the central body of the Commonwealth of Nations, which implements the decisions taken by the association's 54 member governments and organises meetings of Commonwealth ministers. It is headed by a Commonwealth Secretary-General chosen by the Heads of Government for terms of five years, currently (since 2000) former New Zealand foreign minister Don McKinnon.

The Secretariat was established by Heads of Government in 1965, taking over many of the functions of the United Kingdom Government's Commonwealth Relations Office. It is located at Marlborough House in London, a former royal palace which was given by Her Majesty Queen Elizabeth II, Head of the Commonwealth.