As admirers around the world prepared to honour his legacy through a tidal wave of charitable acts, Mandela's youngest daughter said her father was now able to communicate and watch television.
"He is making remarkable progress," Zindzi told Britain's Sky News adding that when she visited him on Tuesday he was "watching TV with his headphones".
"He responds very well with his eyes, and he nods and sometimes he lifts his hand like to shake your hand."
After six often fraught weeks in hospital for South Africa's national icon, that was welcome news to the many South Africans planning to mark his 95 years.
Children in schools around the country will kick off the day by singing "Happy Birthday" to the former statesman, who also marks 15 years since he married his third wife Graca Machel.
Meanwhile biker gangs will clean streets, volunteers will paint schools and politicians will spend 67 minutes on worthy projects - to mark Mandela's 67 years of public service.
"Let us return Madiba's sacrifices and contributions through our own efforts to build a better society," said South African President Jacob Zuma using Mandela's clan name.
Near Pretoria, Zuma himself will try to channel Mandela's cross-community appeal by delivering government housing to poor whites.
The government will also host a ceremony for the symbolic handing over of Mandela's new high-tech ID card, which will be received by Zindzi.
The event is laden with meaning in a country where apartheid was enforced by pass books, which black citizens were forced to carry and which limited movement to certain areas at certain times.
The United Nations declared the Nobel peace laureate's birthday Mandela Day in 2010, but for many this year it takes on extra poignancy.
Mandela has spent the last 41 days in a Pretoria hospital in a critical but stable condition after being admitted for a recurring lung infection.
"There was a time that we were all extremely anxious and worried, and we were prepared for the worst," said Zindzi. "But he continues to amaze us every day."
Breathing with the help of a machine, family and friends have said he is now responding to treatment.
His successor as president, Thabo Mbeki, even suggested he might be discharged from hospital soon.
"I just hope that although he may not be able to enjoy his 95th birthday, that he will be well enough for his 96th," friend and fellow anti-apartheid campaigner George Bizos told AFP.
Elsewhere global luminaries, pop stars and companies also plan to pledge their support for a man who has taken on near mythical status.
'Make the world a better place'
"I will also be giving my 67 minutes to make the world a better place, one small step at a time," British business magnate Richard Branson pledged in a recorded message.
In Manila, 50 abandoned street children will get a television studio tour and see performances by local artists.
On Saturday, Australian city Melbourne will hold a concert featuring local and African artists, while a music festival later this year in Norway will promote equality in schools.
Born on July 18 in 1918, Mandela fought against white rule as a young lawyer and was convicted of treason in 1964.
He spent the next 27 years in jail.
But it was through his willingness to forgive his white jailers that Mandela made his indelible mark on history.
After negotiating an end to apartheid, he became South Africa's first black president, drawing a line under centuries of colonial and racist suppression.
He then led reconciliation in the deeply divided country.
Mandela's peace-making spirit has won him worldwide respect.
"Never before in history was one human being so universally acknowledged in his lifetime as the embodiment of magnanimity and reconciliation as Nelson Mandela," said archbishop emeritus Desmond Tutu, himself a Nobel peace laureate.
But the sunset of his life has been somewhat eclipsed by bitter infighting among his relatives.
A row over his final resting place has seen three of his children's graves dug up and their remains moved, public brawling and legal action among his children and grandchildren.
In a televised address, his grandson Mandla accused a sibling of impregnating his wife and Mandela's oldest daughter Makawize, of sowing divisions in South Africa's most famous family.
Mandela's oldest granddaughter Ndileka spoke of the pain caused by the rift in an interview published Wednesday.
"It was something that we did not want to take in the public space but because of who we are it was, it did spill over to the public space," she told the BBC.
"There is no way that I can never forgive but it's just that right now I'm still hurting."