David Cameron has praised Rowan Williams for his "dedicated service" following the news that he is to step down as Archbishop of Canterbury.
"As a man of great learning and humility, he has guided the church through times of challenge and change," the prime minister said.
"He has sought to unite different communities and offer a profoundly humane sense of moral leadership that was respected by people of all faiths and none.
"As prime minister, I have been grateful for his support and advice and for the work he has done around the world, particularly in Africa where he has taken such a close interest in the Sudan."
"It has been an immense privilege to serve as Archbishop of Canterbury over the past decade, and moving on has not been an easy decision," he said.
Ed Miliband said Williams had challenged "the imagination" of the country during his time as Archbishop.
"Rowan Williams rightly is held in the greatest respect nationally and internationally. He has been an outstanding leader of the church in England and in the wider Anglican Communion in challenging times," he said.
"He has friends on every continent, and has played a vital role in building friendships across faiths and denominations. He has done what he said he would do which is to challenge the imagination of our country.
"I hope he will go on doing that through the rest of his time as Archbishop of Canterbury and beyond in the new role."
One of the Labour leader's key advisers is Tim Livesey, a former aide to the Archbshop. Livesey, 52, served the Williams, first as secretary for public affairs and then as adviser for international affairs.
Deputy prime minister and Lib Dem leader Nick Clegg said Williams had "made an invaluable contribution to public life".
“Like everybody who meets him, I am always struck by how extraordinarily well-informed and measured he is in everything he says," he said.
“He combines an immense gentleness with a sharp and thoughtful mind on a huge number of subjects.
“I have always enjoyed our conversations, particularly in areas of common interest – tackling the stigma of mental health, the reform of our penal system, creating a fair asylum system and promoting human rights.
“I wish him all the best in his new role.”