The Gambia has rejoined the Commonwealth after almost five years outside the institution, fulfilling a pledge made by the country's president.
The West African state left the family of nations in 2013 after then President Yahya Jammeh's administration stated in a televised address the Gambia would "never be a member of any neo-colonial institution".
But a symbolic flag raising ceremony at Marlborough House, the London headquarters of the Commonwealth Secretariat - the institution's civil service, will mark the country's return under the leadership of President Adama Barrow.
Baroness Scotland, the Commonwealth Secretary-General, Francis Blain, the Gambia's high commissioner to London, and senior officials from the Commonwealth will attend the ceremony on Thursday.
The Secretary-General said: "When the Gambia left in 2013, the heads of government expressed their regret in its leaving the Commonwealth family.
"We've looked forward to the Gambia's return and were delighted when, after his election victory in 2016, President Barrow pledged to return.
"The Gambia's application to rejoin has been unanimously accepted by all 52-member states, who welcome back their brothers and sisters to again play their full part in the Commonwealth family."
The decision to begin the re-admission process was made in February last year by President Barrow.
He was the surprise winner of elections in December 2016, beating the incumbent President Jammeh who had come to power in a bloodless coup in 1994.
Last December, the West African nation's parliament unanimously affirmed the country's desire to rejoin the Commonwealth, fulfilling one of the final steps in the organisation's membership process.
Its application was unanimously supported by the Commonwealth's 52-member states and the Gambia will now be invited to attend the Commonwealth Heads of Government Meeting in April in London.
Ahead of his country's return to the Commonwealth Mr Blain said: "I am thrilled to represent my country as it formally rejoins the Commonwealth after an absence of several years - and to become high commissioner rather than ambassador.
"The Government and people of the Gambia will also draw on all that the Commonwealth collectively has to offer, assisting in practical ways to address a wide range of pressing issues - including protecting the environment and tackling climate change, and the empowerment of women and young people."
The Gambia first became a member of the Commonwealth in 1965, when it gained independence from Britain. There are now 53 members of The Commonwealth, representing more than 2.4 billion people.