The freedom fighter died in the United States at the weekend, aged 96.
He was “a brave champion for justice with a lifelong dedication to the cause of non-racialism,” Ramaphosa said.
“We pay tribute to a man of principle and commitment to human rights. But, above all, we remember him for epitomising social solidarity,” the South African leader said.
Born in India in 1924, Reddy joined the anti-apartheid struggle while a student in the 1940s, the presidency said.
He went on to play a leading role on a number of multilateral platforms, agitating for an end to apartheid and for the isolation of Pretoria’s minority regime that treated non-white people as second- and third-class citizens, Ramaphosa said.
In the early 1960s Reddy was secretary of the UN Special Committee against Apartheid and in the late 1970s he was appointed as director of the UN Centre Against Apartheid.
Ramaphosa also commended India, Reddy’s birth place, as the first country to raise its voice against apartheid at the UN in 1946 and Indian leaders and citizens as longstanding friends and allies of South Africans.
Reddy lobbied against apartheid on the world stage for over three decades and developed friendships with a number of leaders of the liberation struggle, including then African National Congress leader OR Tambo.
An ardent admirer of Mandela, he actively campaigned for his release in 1990.
“Besides his own activism, ES Reddy was a prolific scholar whose writing captured, among others, the historical influences of Indian passive resistance on our liberation struggle, and on the political and social realities of democratic South Africa,” Ramaphosa recalled.
He said Reddy believed that speaking and acting against injustice was a moral duty and that all should share “a collective duty to strive towards a world free of oppression and discrimination.”
“It is a struggle that continues today,” Ramaphosa said.
Awarding Reddy with South Africa’s National Order of Companions of OR Tambo (Silver) in 2013 was a fitting tribute to a brave man, the president said.
“We can be gratified that we got to convey our nation’s appreciation to ES Reddy during his lifetime, and to thank him for all what he did for our cause,” Ramaphosa said.