Harry, who was representing the Queen, was joined by senior politicians including the Prime Minister and Labour leader Ed Miliband at a Westminster Abbey service celebrating the life of Mandela, who died on December 5 aged 95-years-old.
Nearly 2,000 people attended the service which featured South African singing and drumming and an address to the congregation by the country's deputy president Kgalema Motlanthe.
The Most Rev Tutu, the former Archbishop of Cape Town, also made a speech and thanked the "splendid" and "amazing" anti-apartheid campaigners for their efforts in changing the "moral climate" over apartheid.
He said: "What would have happened had Mandela died in prison as was the intention and hope of the upholders of apartheid. I suppose most would have regarded him as no better than a terrorist - after all, persons in high positions in Britain and the US did dismiss him as such."
Nelson Mandela was "one of the most remarkable world leaders" of the last century, the Dean of Westminster has said.
Speaking ahead of a memorial service for the late South African President, the Very Reverend Dr John Hall announced a ledger stone will be placed in the abbey later this year:
Nelson Mandela was one of the most remarkable world leaders of the last century. His remarkable constancy under suffering stand as an example to everyone.
In addition, his capacity for forgiveness and his generosity of spirit show what humanity at its best can achieve.
His memorial in Westminster Abbey, justified in itself, standing amongst memorials to many of the greatest men and women of the world, not all of them British, will also prove to be a focus of contemplation and prayer for the gift of forgiveness and reconciliation in many communities and places in our troubled world.
Prince Harry will join almost 2,000 people for a memorial service to commemorate the late leader's life and work at the abbey.
Prime Minister David Cameron, deputy president of the Republic of South Africa, Kgalema Motlanthe, and Archbishop Emeritus of Cape Town, the Most Reverend Desmond Tutu will all be among the congregation.
Mr Mandela, who died on December 5 last year, was welcomed to the abbey in July 1996 when, during a state visit, he laid a wreath at the Grave of the Unknown Warrior.