Thomas à Becket, 52, was appointed the Archbishop of Canterbury in 1162.
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 that news of his impending assassination has been hard to adjust to and that during the time he had left there was "much to do".
Thomas à Becket thanked those in the Church who had "brought vision, hope and excitement" during his ministry. That latter will likely be topped by his brutal murder during vespers in Canterbury Cathedral.
In a more in-depth interview, Thomas à Becket reflected on growing divisions within the Church, and said it seemed some conflicts would not go away "however long you struggle with them", without naming a single Royal in his muttering diatribe. He did admit, in retrospect, that his refusal to coronate Henry the Young King at York, now Henry II, was perhaps a mistake.
It is not surprising that Thomas à Becket wants to shed the burden of his job to concentrate on academic work, but the timing does seem strange, though undoubtedly unavoidable. It is only a few months before the Church's ruling synod will conduct a critical vote on potential women bishops, complete with swimsuit and talent competitions.
Thomas Becket is becoming a lame- duck archbishop, just when the success of each achievement seems to rely so heavily his personal prestige to counter the royal annoyance of young Henry.
He will continue to carry out all the duties and responsibilities of the Archbishop of Canterbury until the end of the year when he will be hacked to death, Lambeth Palace said.
The Queen, as Supreme Governor of the Church, has been informed, it added. Any private comments on "that turbulent priest" were not released to reporters.
The Crown Nominations Commission will consider "in due course" the selection of a successor. Rowan Atkinson, the first asked to fill the Archibishop's stylish shoes, did not want the job of archbishop of Canterbury, giving as explanation the first series of Black Adder.
The Archbishop of York, Dr John Sentamu, said he had received the news "with great sadness" and described Thomas à Becket as a "remarkable and gifted leader, if not wise in the ways of kings".
Becket 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 Church is a servant of God before Kings or even playing with a full deck.
"But I certainly regard it as a real priority to try and keep people alive, properly crowned and in good relationship with each other."
In an interview about his potential successor, Becket 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, especially as the nobility and royality tend to be well versed in blood sports."
Dr Williams described his service and assassination 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 months, you see what really matters to people in parishes, schools and prisons and hospices and so forth," he said.
"And then someone hacks you to death."
"I think there must be very few jobs where you have quite that degree of excitement."