Mohammed Afzal Guru, who was convicted for his role in the terrorist attack on India's parliament in New Delhi in 2001, was hanged after his mercy plea was rejected by President Pranab Mukherjee.
Afzal Guru was hanged at Delhi's infamous Tihar jail at around 8 am local time (2:30 GMT), a senior Indian minister and officials announced.
"Afzal Guru was hanged at 8 am. All legal procedures were followed in the execution. The situation in Kashmir is being closely monitored," said Home Minister Sushil Kumar Shinde.
Afzal Guru was found guilty of facilitating militants to attack parliament.
"The mercy plea of Afzal Guru was rejected a few days ago," said Venu Rajamony, spokesperson of Rashtrapati Bhavan (presidential palace). The body of the militant is to be buried inside the jail, said officials.
The convict, who was working for the Islamic militant group Jaish-e-Mohammed, was originally given the death sentence in 2004. His wife filed a clemency plea with the Indian president in 2006.
"The law has taken its course. The president rejected Afzal Guru's mercy petition on February 3, after which we followed the jail manual and his hanging took place today. His family was informed," said India's Home Secretary R K Singh.
Some human rights activists opined that Afzal Guru was not given a fair trial but most of the political parties supported the death penalty.
The attack on the Indian parliament killed nine people including eight security personnel. Five Islamic militants who stormed the parliament were also shot dead by security forces.
A curfew has been imposed on the sensitive Kashmir region where the news of the hanging is likely to trigger unrest. Television channels have been cut off in some areas to minimise the impact.
India had blamed Pakistan for the attack but Islamabad strongly denied any involvement. The relations between the two countries hit a new low after the attack which evoked widespread anger in India.