Singh, 49, who had been convicted of spying and sentenced to die for bomb blats in Pakistan in 1990, had been the subject of much debate between India and Pakistan, whose relations already are deeply strained over terrorism-related issues, and these discussions had become more intense after Singh was attacked April 26 by two fellow inmates at Lahore's Kot Lakhpat jail. Pakistani authorities have since booked the two inmates.
Since the attack, Singh had been in intensive care at Lahore's Jinnah Hospital even as his relatives and Indian officials had been urging he be sent back to India on humanitarian grounds.
The Press Trust of India news agency, quoting officials, reported Singh died of cardiac arrest at the Lahore hospital after being comatose for nearly a week.
It was earlier reported Singh had slipped into a "non-reversible" coma.
"I received a call from the doctor on duty (at Jinnah Hospital) at 1 am informing me that Sarabjit is no more," Mahmood Shaukat, the head of a medical board that was supervising Sarabjit's treatment, was quoted as saying by PTI.
The news agency quoted another doctor who had been a member of a team treating Singh as saying he died of cardiac arrest and that doctors made several unsuccessful attempts to resuscitate him. The report also quoted Indian Embassy officials in Islamabad as saying they had been informed by hospital officials about his death.
Pakistan's Express Tribune said Singh had suffered head injuries during his beating. The report said his death came just after his family members returned to India after spending three days in Pakistan.
Pakistan's Dawn newspaper reported Singh's attorney, Owais Sheik, also confirmed the death and said his body "has been moved to the hospital mortuary." An earlier Dawn report said Singh had been attacked with bricks and other blunt weapons.
The report said a medical board set up for his treatment had put him on a ventilator. As regards the spying charge against Singh, his family had maintained he was a victim of mistaken identity and he had inadvertently strayed across the border, the report said.
Earlier, Singh's sister Dalbir Kaur told newsmen at the border Pakistani authorities should look into how his security was compromised, Dawn reported.
It quoted the Pakistan Foreign Ministry as saying Indian diplomats were given access to Singh on two occasions.
Singh's mercy petitions were rejected by courts and former President Pervez Musharraf, the report said. His execution, however, had been put off indefinitely by the next civilian government, which completed its five year term in March.
PTI said Pakistani authorities were yet to decide whether there would be an autopsy on Singh's body.
Among Singh's other survivors are his wife and two daughters.