"In his death, South Africa has lost a leader and conscience keeper. India has lost a true friend who commanded universal admiration and respect," he said.
The deputy leader of Congress in Rajya Sabha said Kathrada, known as Kathy, spent over 26 years in prison, and was resolute in fighting for freedom and justice for the oppressed people of South Africa.
He said at the Robben Island prison, Kathrada meticulously documented the history of African National Congress's (NAC) struggle against apartheid, and continued his academic and literary pursuits obtaining four University degrees.
He said Kathy was an inspiration to people of South Africa and a hero to freedom loving people throughout the world.
"We deeply mourn the death of one of the greatest freedom fighters of the 20th century and a prisoner of conscience," he said.
Kathrada, 87, died at the Donald Gordon Hospital at Johannesburg after complications following a brain surgery today, his foundation said.