Archbishop of Canterbury Dr Rowan Williams has announced he is to stand down in December.
He will take the position of Master of Magdalene College at the University of Cambridge from January next year, his website says.
Dr Williams, 61, was appointed the 104th Archbishop of Canterbury in 2002.
In a statement on his website, the head of the 85 million-strong Anglican Communion said serving as archbishop had been "an immense privilege".
He said stepping down had not been an easy decision and that during the time he had left there was "much to do".
Dr Williams thanked those in the Church of England and the wider Anglican Communion who had "brought vision, hope and excitement" during his ministry.
In a more in-depth interview, Dr Williams reflected on growing divisions within the Anglican Church, and said it seemed some conflicts would not go away "however long you struggle with them".
Under his leadership, the Church of England has come close to splitting over the ordination of gay clergy and women bishops. Dr Williams has consistently supported the ordination of women, and previously showed no objection to the appointment of an openly-gay bishop in Reading.
Dr Williams also reflected on his controversial remarks in 2008 that adoption of certain aspects of Sharia law in the UK seemed "unavoidable," saying he stood by his argument.
He will continue to carry out all the duties and responsibilities of the Archbishop of Canterbury, both for the Church of England and the Anglican Communion, until the end of the year, Lambeth Palace said.
The Queen, as Supreme Governor of the Church of England, has been informed, it added.
The Crown Nominations Commission will consider "in due course" the selection of a successor.
The Archbishop of York, Dr John Sentamu, said he had received the news "with great sadness" and described Dr Williams as a "remarkable and gifted leader".
Prime Minister David Cameron said Dr Williams had "guided the Church through times of challenge and change" and praised the work he had carried out around the world, including in Africa. Last October Dr Williams delivered a sermon in Zimbabwe as part of an African tour to try to heal divisions within the Anglican Church.
His resignation marks the end of more than 20 years as a bishop and archbishop. His predecessor, Lord Carey, held the post for 11-and-a-half years and retired at the age of 66 in 2002.
Dr Williams has also been pivotal to national events, including the Royal Wedding at which he married the Duke and Duchess of Cambridge at Westminster Abbey in 2011.
His departure comes after tensions within the Anglican Communion over the issue of homosexuality and women bishops.
Dr Williams said: "The worst aspects of the job, I think, have been the sense that there are some conflicts that won't go away, however long you struggle with them, and that not everybody in the Anglican Communion or even in the Church of England is eager to avoid schism or separation.
"But I certainly regard it as a real priority to try and keep people in relationship with each other."
Responding to the announcement of his retirement, Church of England General Synod member Alison Ruoff said: "He's a kind, wise, warm, godly man, but had he actually stood up and been counted as a leader, I think we would be in a very different place in the Church of England from where we are now, and that is thoroughly regrettable."
In an interview about his potential successor, Dr Williams said: "I think that it is a job of immense demands and I would hope that my successor has the constitution of an ox and the skin of a rhinoceros, really.
"But he will, I think, have to look with positive, hopeful eyes on a Church which, for all its problems, is still for so many people, a place to which they resort in times of need and crisis, a place to which they look for inspiration."
Dr Williams described serving as archbishop as an "enormous privilege".
"The privilege is that you are taken into the heart of the local church's life for a few days, you see what really matters to people in parishes, schools and prisons and hospices and so forth," he said.
"I think there must be very few jobs where you have quite that degree of open doors for you."
He said he did not believe that Christianity was losing the battle against secularisation in Britain.
"I think there is a great deal of interest still in the Christian faith," he said.
Dr Williams becomes the 35th Master of Magdalene College from January next year.