Singh was arrested following a bombing in Lahore in 1990 in which 14 people were killed.
He was sentenced to death after being convicted by a court but his family had previously filed mercy petitions to Pakistani authorities seeking his release, maintaining that Singh is a victim of mistaken identity and had inadvertently strayed across the border.
However, the Pakistani security agencies says that Singh had admitted that he was sent to Pakistan to carry out serial bomb blasts in Lahore, Faislabad, and Kasur, and was trained by the Indian Army, and the Research and Analysis Wing (RAW).
Singh was awarded the death sentence by a Lahore anti-terrorism court in October 1991.
He challenged the verdict in the Supreme Court, however, the apex court quashed his appeal in September, 2005, saying that the review petition was not filed within the time period as mentioned in the law.
In March 2006, a two-member Supreme Court bench dismissed Singh's petition against his conviction in the Lahore's Yakki Gate bomb blast in 1990.
Since then he was languishing in jail, as Pakistan has denied setting him free, despite efforts by the Indian diplomatic channels.
Sarabjit was assaulted in Lahore jail six days back and he was declared dead at 1.30 am, May 2.