Lord Patten has stood down from his role as chairman of the BBC Trust for health reasons after a turbulent three years in the job.
The former Cabinet minister's stint at the top of the BBC's governing body, which started in 2011 and was due to end next April, has seen him work with three different director-generals and weather scandals including excessive executive pay and the corporation's disastrous Diamond Jubilee coverage.
L ord Patten, who had heart surgery seven years ago, said he underwent further surgery last month after being admitted to hospital in London with "serious chest pains".
He paid tribute to the medical staff who treated him, saying: "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, and that I should reduce the range of roles I undertake.
"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. This is a position that requires and has received from me 100%, and has 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. I have to begin by taking a six-week break from any work at all."
His departure comes as the BBC faces further fallout from the Dame Janet Smith review into the corporation's "culture and practices" while disgraced DJ Jimmy Savile worked there.
That scandal and the BBC's reaction to it lead to the resignation of director-general G eorge Entwistle - seen as a close ally of Lord Patten - after just 54 days in the role and was seen as a blow to his authority.
In a statement, L ord Patten said: "It has been a privilege to have served as chairman of the BBC Trust. Like the NHS, the BBC is a huge national asset which is part of the everyday fabric of our lives. It is not perfect - what institution is? It always needs to challenge itself to improve. But it is a precious and wonderful thing, a hugely positive influence which benefits greatly from the creativity and dedication of its staff.
"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. Most important of all, the British public enormously value the strength of its output, its independence and the contribution it makes every day to the quality of our lives.
"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. For the time being, however, I shall be making no further statement whatsoever about the BBC or my period as chairman of the BBC Trust."
His departure will re-open the debate around how the BBC is governed - Conservative MP Michael Fabricant tweeted: "The Chairman of the BBC needs to be alert to issues. Not a superannuated grandee detached from modern reality."
A report last year by the Public Accounts Committee on the executive payoff scandal said the affair showed "a dysfunctional relationship" between BBC management and the Trust and said "the governance model is broken".
One of Lord Patten's most fierce critics on the Culture, Media and Sport Committee, Philip Davies MP, said: "Always wanted to see Lord Patten leave the BBC Trust but not in these circumstances. I wish him well with his recovery and recuperation."
Director-General Tony Hall said: "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."
Vice-chairman Diane Coyle, who is the wife of BBC technology correspondent Rory Cellan-Jones, will take over as acting chairman until a successor is appointed.
In his letter to Lord Patten, Culture, Media and Sport Secretary Sajid Javid said he accepted his resignation with "regret".
He wrote: "Over the last three years, under your chairmanship, you have steered the Trust successfully through some great moments for the BBC, including coverage of the Olympics and continuing to deliver high quality original programming that is exported around the world.
"You have also embraced the challenges that have confronted the BBC, putting in place improvements to governance and building a stronger executive team helping the BBC to move forward with confidence.
"Throughout, you have shown an unfettered personal commitment to securing the best outcome for the public."
Shadow culture secretary Harriet Harman said: " Lord Patten became trust chair at a difficult time in its history and helped the BBC to turn a corner under new leadership with Tony Hall. He proved himself a firm friend of the BBC and its values and set the corporation on a strong track towards licence renewal.
"We wish him well in his recuperation.
"The BBC is a hugely important British institution and we look forward to a strong successor with the authority and leadership to see the BBC through to charter renewal."