Mr Venkataraman was an "outstanding figure", the prime minister said
Ramaswamy Venkataraman, who helped to draft India's constitution and served as president from 1987 to 1992, has died at the age of 98.
Mr Venkataraman was admitted to the hospital on 12 January but his condition deteriorated, a government statement said.
Announcing seven days of mourning, Prime Minister Manmohan Singh said India had lost an "outstanding figure".
Mr Venkataraman was an MP in the first parliament and also a vice-president.
Tough tenure
Mr Singh said: "The former president will be long remembered for his service to the nation, the strength of character and his knowledge and wisdom."
Current President Pratibha Patil said India had lost a true patriot.
"He served with distinction in various capacities in public life and ultimately rose to occupy the highest office of the nation," she said.
"In his passing away, the nation has lost a distinguished luminary."
A Tamil Nadu native, Mr Venkataraman's tenure as president coincided with the Sri Lanka crisis, the Bofors Gun deal and the assassination of Rajiv Gandhi.
Mr Venkataraman died on Tuesday with his wife and son-in-law in attendance at the Army Hospital (Research and Referral) in Delhi.
The cabinet has said there will be a state funeral.
Ramaswamy Venkataraman
The 8th President of India, Ramaswamy Venkataraman has died at the age of 98. Venkataraman served as President from 1987 to 1992, he was also the Vice President of India from 1984 to 1987. He was admitted to hospital on the 12th of January and stayed there until his death on the 27th. He was complaining of Urosepsis, a condition caused by the extravasation of urine. His condition turned critical on January 20. 

Born in Pattukkottia he graduated from Madras University studying Economics. 

In 1980 he succeeded Choudhary Charan Singh as the Union Finance Minister of India and then Vice President under President Zail Singh. He later became the 8th President of India. During his run as President he faced troubles such as the Sri Lanka crisis, the Bofors Gun deal and the assassination of Rajiv Gandhi.  He was succeced by Shankar Sharma. 

With the death of Venkataraman, Abdul Kalam becomes the only surviving former Indian President. Indian Prime Minister Manmohan Singh said India had lost an outstanding figure. A state funeral will be held says the cabinet.