Mandela, South Africa's first black president, who steered his nation out of apartheid and into multi-racial democracy, died last Thursday at the age of 95 after months of illness.
Since then, the country has been gripped by an outpouring of emotion unrivalled since Mandela's release from 27 years of prison in 1990 and his subsequent election victory. Crowds have piled flowers, candles, balloons and messages outside his Johannesburg home.
In New Delhi, Singh paid tribute to Mandela by writing his thoughts about one of the most charismatic and influential leaders of the 20th century in a condolence book placed at the South African High Commission.
In India, Mandela is highly revered for adopting methods of non-violence and peace to achieve his political objects against the apartheid system, which were espoused by Mahatma Gandhi, the man who led India to its independence by peaceful and non-violent means.
Mandela rose from rural obscurity to challenge the might of white minority rule - a struggle that gave the 20th century one of its most respected and loved figures.
He was elected President in landmark all-race elections in 1994 after helping to steer the racially divided country towards reconciliation and away from civil war.
Mandela was awarded the Nobel Peace Prize in 1993, an honour he shared with F.W. de Klerk, the white Afrikaner President who released him in 1990. Reacting to his death, the Nobel Committee said Mandela would remain one of the greatest ever prize winners.
The former South African President was one of the three persons of non-Indian origin and the second non-citizen to be awarded the Bharat Ratna, the country's highest civilian honour in 1990.
Fifty-nine foreign heads of state or government have said so far they will attend either the memorial ceremony or the state funeral of Nelson Mandela in South Africa in the coming week, a South African foreign ministry spokesman told Reuters.