"Your victory has demonstrated that no person anywhere in the world should not dare to dream of wanting to change the world for a better place," the anti-apartheid icon wrote to Obama in a letter released by the Nelson Mandela Foundation.
"We note and applaud your commitment to supporting the cause of peace and security around the world. We trust that you will also make it the mission of your Presidency to combat the scourge of poverty and disease everywhere."
Kenyans in Barack Obama’s ancestral homeland danced with joy on Wednesday and the election of America’s first black president sparked hope that he would tackle poverty and disease in Africa.
As a pink dawn lit the sky, hundreds in a field at Obama’s late father’s village clapped and cheered when key swing states fell to east Africa’s favourite adopted son.
"We are going to the White House! We are going to the White House!" relatives sang at the top of their voices as they danced around the family’s modest homestead in Kogelo, pausing only to hug each other and hoist small children into the air.
In the tiny village in western Kenya where Obama’s 87-year-old grandmother lives, family members prepared to roast a bull in celebration while villagers swarmed the family home, banging drums, ululating and waving tree branches.
Born in Hawaii to a white mother from Kansas and a Kenyan father, Obama is idolised by many Africans the way the Irish saw U.S. President John F. Kennedy in the 1960s: as one of their own who succeeded beyond their wildest dreams.
Many Africans fervently hope his victory will mean more U.S. support for local development and an improvement in living conditions for the majority on the world’s poorest continent.
Analysts have cautioned, however, that Obama may have little scope to bring tangible benefits to Africa, and that he does not have a strong track record of interest in the continent.
Wars in Iraq and Afghanistan along with healthcare reform and the financial crisis at home are likely to take up his time.
During a previous visit to western Kenya in 2006, Obama reminded thousands of adoring fans that he was the senator for Illinois in the United States — not Kogelo.
Africa’s largest nation, Sudan, was quick to dismiss any notion a Democrat president with African roots would make much difference to its troubled relationship with Washington, particularly over the festering Darfur conflict.
"When it comes to foreign policy there is no difference between the Republicans and the Democrats," said Foreign Ministry spokesman Ali al-Sadig.
But across Kenya there were celebrations and President Mwai Kibaki declared Thursday a national holiday in honour of Obama.
The Harvard-trained lawyer and civil rights activist enjoys rock star status in the east African nation. Babies have been named after him, drinkers knock back "Senator" beers in his honour, pop stars sing his praises and "Obama: The Musical" opened in the capital Nairobi on Sunday.
In the southern nation of Zambia, Obama’s win fuelled hope the world’s poorest continent was set for a change of fortune.
"Obama’s victory is as sweet as a well-prepared African meal of vegetable and peanuts. Only a few years ago, it was unthinkable to have an African-American in the White House," said Jane Phiri, 42, a vegetable vendor in the capital Lusaka.
"But now it is a dream come true and I am sure Obama will not forget his ancestral home."