Sir Michael Lyons will step down as chairman of the BBC Trust in May, explaining that the job has become all-consuming and that he does not want to stand for a second term.
The Trust chairman has written an open letter to culture secretary Jeremy Hunt to explain why he is not going to seek re-election to a body that has made some difficult and controversial decisions over the past 12 months.
"For all the positives associated with this agenda, I have to acknowledge that the role of chairman has been far more demanding than the nominal three to four days a week in the job specification," explains Lyons.
"It is of course a compelling aspect of working at the BBC that it can become an all-consuming part of one's life – and this applies equally to the staff across the BBC whose great commitment helps underpin its position as the world's leading public broadcaster," his letter continues.
"But this workload has now reached a point where I am increasingly concerned that it is crowding out other appointments to which I remain committed and other activity that I wish to undertake."
The BBC Trust's role as the watchdog to the licence-fee funded BBC has proven increasingly difficult as the media world swells beyond radio and television broadcast.
Lyons' reign includes the still controversial decision to rubber stamp Project Canvas – a decision loudly criticised by some of the nation's biggest platforms, including Virgin Media and BSkyB.
Lyons will step down in May, and his replacement is likely to be a high-profile figure.