Dr Rowan Williams is to become chairman of the board of trustees at Christian Aid from next year.
Announcing the appointment today, Christian Aid director Ms Loretta Minghella said: "Archbishop Rowan brings a passionate interest in tackling the symptoms and causes of poverty, a profound theological understanding and deep experience of addressing issues of environmental, economic and social justice with church and political leaders across the world. This is wonderful news for Christian Aid."
Dr Williams is stepping down as Archbishop of Canterbury at the end of December to take up a new position as Master of Magdalene College, Cambridge.
He succeeds Dame Anne Owers as Chair of the Christian Aid board.
Commenting on his new appointment, Dr Williams said: "I am very honoured indeed to be invited to chair the Board of Christian Aid.
"I had hoped very much to be able to continue some regular involvement in support and advocacy in the area of international justice and development, and this will allow such an involvement to flourish.
"Many years of co-operation with, and support for, Christian Aid have made me familiar with the excellent quality of all that they do, and I am personally very happy indeed to be working with them in this new role at a time when international development issues will need the most dedicated and sustained attention."
The appointment process was led by Kumar Jacob, Acting Chair of Christian Aid's board, and culminated in a process of approval this week by Christian Aid's sponsoring churches.
Mr Jacob said: "Archbishop Rowan's leadership on issues of international development and the role of churches in the fight against poverty across the world has been exceptional.
"I believe we have found in him the perfect Chair for the organisation at this time and a great custodian for the British and Irish churches' continuing work in tackling the scandal of poverty through their support for Christian Aid."
Mr Jacob will continue as Acting Chair until Dr Williams takes up his position in May 2013.