Nelson Mandela is to open Southwark Cathedral's new cloister buildings after a dedication service on Saturday 28 April.
The former South African President will also name a room in honour of Archbishop Desmond Tutu who once served in the Southwark Diocese.
"We are humbled and thrilled that Nelson Mandela, probably the most outstanding man of our times, has agreed to visit us and open these buildings" says Dean of Southwark Colin Slee.
"He is renowned for his suffering, passion for justice and almost unimaginable compassion and forgiveness.
"It is not inappropriate that he should lend his support to Southwark Cathedral as our work is dedicated to expanding our ministry to an area that has always been outcast in terms of London's wealth, the place to which socially marginalised people have come for sanctuary and assistance."
The £10.2 million development is partly funded by a Millennium Lottery grant of £4.2 million. The appeal was launched in 1999 by Archbishop Tutu.