Williams, who was chosen by Prime Minister Tony Blair, succeeds the Most Rev. George Carey, who is retiring on Oct. 31 after 11 years.
"If there is one thing I long for above all else, it is that the years to come may see Christianity in this country able again to capture the imagination of our culture, to draw the strongest energies of our thinking and feeling," Williams said at a news conference after his appointment was announced.
CBS News Chief European Correspondent Tom Fenton reports Williams will be somewhat of a change from his predecessor. He's known to be a liberal, especially on the two questions that have most bothered the church, the ordination of women priests and of homosexual priests.
Williams has labeled the Afghanistan conflict "morally tainted" and said any U.S. invasion of Iraq would be "immoral and illegal." He has criticized the Blair government.
He is even ready to step into a moral minefield. Aides say he would allow Prince Charles and his longtime lover Camilla Parker Bowles, both divorcees, to marry in church.
Unlike most of his clerics, Williams is also said to be keen to sever the links between state and church in Britain, where vicars swear allegiance to the crown.
On the lighter side, the bearded cleric who looks like Moses in a Cecil B. DeMille epic has a passion for The Simpsons on television, calling them "one of the most subtle pieces of propaganda around in the cause of sense, humility and virtue."
As Archbishop of Canterbury, he is the head of the worldwide Anglican Communion, which includes the Episcopalian church in the United States and some 70 million people around the world.
Williams, 52, has been praised in some church quarters as an orthodox Christian and a deep thinker. Desmond Tutu, the former archbishop of Cape Town, describes Williams as "the leading theologian in our communion." But some conservatives have been alarmed that he admitted ordaining a priest whom he suspected of living in a homosexual relationship.
Williams, who was in lower Manhattan on Sept. 11 as terrorist strikes brought down the World Trade Center, has criticized the U.S.-led war on terrorism, and has condemned sanctions against Iraq and the American threats of military action against Saddam Hussein.
Writing recently about the war on terrorism, Williams said, "It is just possible to deplore civilian casualties and retain moral credibility when an action is clearly focused and its goals are on the way to evident achievement.
"It is not possible when the strategy appears confused and political leaders talk about a war that may last for years."
He recently signed a declaration denouncing any U.S. plans to attack Iraq, arguing that "eradicating the dangers posed by malevolent dictators and terrorists can only be achieved by tackling the root causes of the disputes."
That stance was an echo of his "peacenik" past — Williams was arrested in 1985 while reciting psalms on the runway of a U.S. airbase in Britain.
For Episcopalians in the United States, it will mean a more sympathetic ear from the spiritual head of their church for the ordination of homosexual priests and for women priests, which the Episcopalian Church in the United States has had for some years, reports Fenton.
Williams was born in Wales in 1950 to a Welsh-speaking family and became Oxford University's youngest theology professor at the age of 36. He was enthroned as Bishop of Monmouth in 1992 and elected Archbishop of Wales in 2000.
He is the first Archbishop of Canterbury from outside England since the 16th century breakaway from Rome.
Vividly recalling the surreal silence of the horror, he said: "It can't have been silent. There must have been — I know there were — shouts, sirens. A few minutes later there was an indescribably long roar of the second tower collapsing. But I remember it as quiet; the very few words spoken, the ghostliness of it all."
Williams takes the helm of a Church of England which is suffering a steep long-term decline in attendance and increasing pressure on its financial resources. He has advocated "disestablishment" — ending the church's privileged position as England's legally established church, whose supreme governor is the monarch.
"I think the church is in for an exciting ride with someone who is not defensive and who is open and who will engage with contemporary issues," Christina Rees, a member of the governing General Synod of the Church of England said Tuesday.
Frank Naggs, a conservative evangelical member of the General Synod, told the BBC his group had "problems with his radical agenda, but in the Christian way we would like to have him clarify some of these issues, so we are arranging an early meeting hopefully to clarify some of these fundamental concerns."
On ordaining homosexual priests, he added: "As far as we are concerned it's against the Biblical revelation ... and we are prepared to go to the wall on this one."
Williams was quoted this year as saying it was not his job to be "going around the bedroom with a magnifying glass doing surveillance." And he said it was not necessary for homosexual priests to be celibate "in every imaginable circumstance."
Williams, whose wife Jane is a theology lecturer, has two children and cheerfully admits he is too busy getting them ready for school to find any time to pray in the morning.