And despite his limited time as a bishop, Welby was considered as a frontrunner to step into Williams' shoes in recent months.
The question of who would succeed the scholarly archbishop had been the subject of intense speculation among members of the Anglican Communion and others since Williams announced his intention to stand down in March.
Potential contenders for his role were considered by the Crown Nominations Commission, which made a recommendation to Prime Minister David Cameron. Cameron then gave a recommendation to Queen Elizabeth II, who formally appoints the archbishop of Canterbury as supreme governor of the Church of England.
Many within the church will look to Welby to give a clear voice on divisive issues to help lead the Anglican Communion forward.
In a letter to the Crown Nominations Commission in July, the leadership of the Global South pointed out that its members make up about 55 million of the number worldwide, and made an appeal for the new archbishop to foster unity and uphold the "orthodoxy of the Christian faith."
"Anglicans today stand in worship and witness amidst diverse cultures, among ancient traditions and often in inter-religious tensions," the church leaders wrote.
"The new Archbishop of Canterbury should have the experience and cross-cultural sensitivity to understand the concerns and conflicts in the worldwide Communion. He has to be able to communicate effectively with and gain the respect and confidence of, his fellow Primates in the Global South."
The new archbishop must also "be able to build upon the work of his predecessors while avoiding any further actions that may widen the gap between us and these partners," the letter stressed.
Williams, who said "moving on has not been an easy decision," has accepted the position of master of Magdalene College at Cambridge University starting early next year.
The secretary-general of the Anglican Communion, Canon Kenneth Kearon, said Williams' time in office had "coincided with a period of turmoil, change and development in the Anglican Communion, and his careful leadership, deeply rooted in spirituality and theology, has strengthened and inspired us all in the Communion during this time."
Although Williams came out against gay marriage, speaking of the dangers -- as he called them -- of "imposing" this on the rest of the population, he is generally perceived to be a liberal and is credited with pushing forward the ordination of women bishops, which had been a major controversy.
Among others considered likely to take over from Williams were the Ugandan-born archbishop of York, John Sentamu, and the bishops of Coventry and Norwich.
Born in London in 1956, Welby has five children aged 16 to 27 with his wife, Caroline. They lost their first child, a daughter born while they lived in Paris, to a car accident in 1983, according to a biography on the website of the Durham diocese.