Williams, 61, plans to return to the academic world as master of Magdalene College at Cambridge, The Guardian reported. In an interview, he described the difficulties of leading a church split by disagreements on homosexuality and the role of women.
"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," Williams said.
The church must now pick a successor. English bookmakers appear to be putting their money on Archbishop of York John Sentamu, 62, who was born in Uganda and would be the first African to head the church.
Bishop of London Richard Chartres, 63, who opposes ordaining women, is another possible candidate.