The BBC`s director general, Mark Thompson, has told staff he will leave the corporation this autumn, according to BBC.
With nearly eight years in the job, he has been the BBC`s longest-serving director general since the 1970s.
His tenure has seen the BBC suffer scandals including the Sachsgate affair and a series of budget cuts and staff redundancies.
But he has also presided over successes including Strictly Come Dancing and Frozen Planet.
Mr Thompson was appointed in May 2004. He took over in the wake of Greg Dyke`s resignation, following criticism of the BBC in Lord Hutton`s report on the death of the government weapons inspector Dr David Kelly.
As director general, he is responsible for the BBC`s services across television, radio and websites and for a global workforce of 20,000.
His departure was not unexpected. In January, Lord Patten, who runs the BBC Trust, said the corporation was engaged in "sensible succession planning" to find a replacement.
In an email on Monday, Mr Thompson paid tribute to staff, and called the BBC "the best broadcaster in the world".
"We`ve weathered a series of lively storms and been through some trying, as well as some very successful, times together.
"What has made my job not just bearable, but immensely enjoyable and rewarding, is all of you: Your talent and energy, your unshakeable belief in the BBC and everything it stands for."
No specific date has been set for his departure - but Mr Thompson said he would remain at the corporation until coverage of the 2012 Olympics and the Queen`s Jubilee has been completed.
His timing was also influenced by the looming review of the BBC`s Royal Charter. The current charter, which expires in 2016, sets out how the BBC should be funded, what it does and how it is managed.
"We can address the exact date of the handover once an appointment is made," he said, "though I have made it clear that I want to be guided by the wishes of the Trust and of my successor, whoever that may be."
In a statement, Lord Patten said Mr Thompson had been an "outstanding" leader.
"He took over during a traumatic period in the corporation`s history and subsequently enhanced its reputation for creativity and quality, while setting the course for the BBC`s digital future.
"I will miss him on both a personal and professional level and I wish him the very best of luck for the future."
There is already speculation over Mr Thompson`s successor, with many media pundits suggesting the BBC will appoint its first ever female director general.
Possible candidates include Helen Boaden, head of BBC News, Caroline Thomson, the BBC`s chief operating officer, and ITV`s current director of television, Peter Fincham.
However, the successful applicant will have to settle for a smaller salary than the £671,000 remuneration package earned by Mr Thompson, as part of a long-standing pledge to cut senior management costs at the corporation.