On Thursday, before a meeting in London of the Group of Seven (G7) finance ministers, the political prisoner turned world diplomat told a cheering crowd of 22,000 people in Trafalgar Square that now was the time for decisive action.
Looking frail, and supporting himself with a stick and with his wife, Graca Machel, holding his other arm, Mandela descended the steps towards the podium with evident difficulty.
But his voice was firm and clear when he told the rally: "Massive poverty and obscene inequality are such terrible scourges of our times ... that they have to rank alongside slavery and apartheid as social evils.
"In this new century, millions of people in the world's poorest countries remain imprisoned, enslaved and in chains. They are trapped in the prison of poverty. It is time to set them free."
The crowd of young and old with banners and whistles cheered loudly as they stood under leaden skies in front of South Africa House that was for decades a symbol of the evils of apartheid.
British Prime Minister Tony Blair has vowed to make Africa one of the priorities of his presidency of the G7 industrialised nations this year.
Mandela (C) is to talk to Brown(L)
about tackling world poverty
Adult prevalence of HIV/Aids in sub-Saharan Africa is the highest in the world at 7.5% against a world average of 1.1%, according to the United Nations.
Life expectancy at birth in 2003 was 46 years against a world average of 63 and, while globally life expectancy has risen by seven years since 1970, it has actually fallen in 18 African countries over the same period.
Mandela is expected to take his message to the finance ministers when British Chancellor of the Exchequer Gordon Brown opens the meeting on Friday.
Although he formally declared his retirement from politics and diplomacy last June just before his 86th birthday, Mandela said he could not ignore the call to help Africa's poor.
"I recently formally announced my retirement from public life and should not really be here," he said on Thursday.
"Recognise that the world is hungry for action, not words. Act with courage and vision"
"However, as long as poverty, injustice and gross inequality persist in our world, none of us can truly rest."
He was speaking as part of the charity-driven Make Poverty History campaign.
"In 2005, there is a unique opportunity for making an impact," said the Nobel peace laureate who spent nearly 27 years in apartheid jails before becoming the country's first black president from 1994 to 1999.
"Do not look the other way. Do not hesitate. Recognise that the world is hungry for action, not words. Act with courage and vision," he said.