In a statement Lord Patten said he’d taken the decision following major heart surgery in late April.
Doctors at Royal Brompton Hospital successfully carried out a procedure involving a combination of bypass surgery and angioplasty which ensured “no permanent damage” to Patten’s heart.
However the former Conservative minister said: “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 per cent commitment, 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.”
Patten has tendered his resignation to Culture secretary Sajid Javid who will be responsible for the appointment of a successor.
In the meantime the BBC Trust will be led by Vice Chair, Diane Coyle.
Lord Patten took up the post as BBC Trust Chairman in May 2011 and his term was due to end in April 2015.
Commenting on Lord Patten’s announcement, Tony Hall, BBC Director-General, 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.”