Video report by ITV News Political Correspondent Libby Wiener
The Chairman of the BBC Trust Rona Fairhead is to step aside after two years in the role, the organisation has confirmed.
In May, following the publication of the BBC White Paper, she was asked to continue in the role for four more years by David Cameron's government.
She will remain in the role until someone is appointed chair of the new board, which will replace the trust.
In a statement, the former head of the Financial Times said she decided to quit rather than take part in the reapplication process for the role.
BBC director-general Tony Hall said: "Rona has made a real contribution to the BBC and at a really important time for us.
"On behalf of all the staff, I'd like to thank her for that and wish her the very best for the future. We will continue to work together in the interests of licence fee payers until the new governance arrangements are in place."
Ms Fairhead has held the role since October 2014.
In March a review concluded the BBC Trust should be abolished and regulation of the corporation handed to Ofcom.
Sir David Clementi, who led the review into how the BBC is governed, said the trust was "flawed" and "fundamental reform" was needed.
Last year, the Chair of the Public Accounts Committee, Margaret Hodge, urged Ms Fairhead, who was also HSBC non-executive director, to stand down as BBC Trust chair following the bank's tax avoidance scandal.
A spokesman for the Department for Culture, Media and Sport said: "The Government thanks Rona Fairhead for her service to the BBC.
"Full details of the BBC Charter will be announced shortly."