President Pratibha Patil and Prime Minister Manmohan Singh mourned the death after prolonged illness of Communist veteran Harkishan Singh Surjeet on Friday afternoon.
While the president's office sent a condolence message, the prime minister described the late leader as a "great patriot".
Manmohan Singh, who reached Colombo on Friday to attend the SAARC summit, said the Marxist veteran was a "friend, guide and supporter".
Remembering Surjeet's role in bringing various political parties together to form a coalition, Manmohan Singh said he was the architect of the ruling United Progressive Alliance (UPA).
Surjeet, who had been the Communist Party of India-Marxist (CPI-M) general secretary from 1992-2005, died after a cardiac arrest at 1.35 p.m. at the Metro Hospital in Noida.
Communist Party of India (CPI) leader D. Raja said Surjeet's death was a "big loss".
Observing that the departed leader was a "great inspiration", CPI-M leader Nilotpal Basu said: "He played a pivotal role in bringing together different political parties and changing the political scenario."
Added Mohammed Salim, a CPI-M MP from West Bengal: "He developed a young band of communist leaders, who are politically aware, unlike others who promote their daughters, sons and in-laws. He was a very hard working person and did not waste any time. He built the party and the movement and fought against divisive communal forces.