Lord Patten, the chairman of the BBC Trust, is to stand down with immediate effect following major heart surgery.
Patten will be replaced by vice-chairman and former Treasury adviser Diane Coyle until a successor is found.
"On the advice of my doctors, however, and having consulted my family and friends, I have concluded that I cannot continue to work at the same full pace as I have done to date," Patten said in a statement.
"On this basis I have decided with great regret to step down from much the most demanding of my roles – that of chairman of the BBC Trust.
Patten, whose work sees him oversee BBC management, said that he has undergone a combination of bypass surgery and angioplasty with success.
However the 69-year-old added that the position of chairman "requires and has received from me 100% commitment, and had been my priority at all times.
"It would not be fair to my family to continue as before and equally it would not be fair to the BBC and those it serves not to be able to give that commitment which the role demands," he said.
Patten’s tenure has been blighted by the Jimmy Savile scandal and massive executive payoffs.
But while he admitted that the BBC is not "perfect" he said that, like the NHS, it is a "huge national asset which is part of the everyday fabric of our lives".
"I have had no reason to doubt that the leaders of all main political parties support the role it plays at the centre of our public realm," he said. "When in due course the future of the BBC is subject to further discussion at charter review time, I hope to say more on the issue."
The BBC director general, Tony Hall, said in a statement: "I have enjoyed working with Chris over the last year; he is a staunch believer in the BBC and he has brought his vast experience to the role of chairman of the BBC Trust. He has steered the BBC through some of its most difficult days. In undertaking this role he brought unrivalled experience, wisdom, and an overwhelming desire to ensure that the BBC remains the best public service broadcaster in the world."