The Prince of Wales will be the next head of the Commonwealth, the BBC understands.
The Queen had said it was her “sincere wish” that Prince Charles would succeed her in the role “one day”.
Leaders of the Commonwealth have been discussing the issue at a meeting behind closed doors at Windsor Castle.
The non-hereditary role would not have automatically passed to Prince Charles, with some suggestions it might rotate among the 53 leaders.
The BBC’s diplomatic correspondent James Landale said a source had told the BBC that Commonwealth leaders had agreed the appointment.
Prime Minister Theresa May and Canadian PM Justin Trudeau had earlier given their backing to Prince Charles.
The meeting during a two-day summit involved 46 heads of Commonwealth governments and foreign ministers from the remaining seven countries.
The Commonwealth represents about 2.4bn people, but critics say the organisation is so disparate that it struggles to know what it is for, BBC royal correspondent Jonny Dymond said.