Mr Karunanidhi said that Home Minister Sushil Kumar Shinde's "assurance to examine requests by the Punjab Chief Minister to reconsider the Bhullar case is reassuring."
"Badal ji and his son handed over the same representation that was given to PM, President. It is under consideration," he said.
The Akali Dal-led government in Punjab has sought that the death penalty awarded to militant Devender Singh Bhullar, convicted for a car blast in Delhi that killed nine people in 1993 be commuted to life imprisonment.
Last week, the Supreme Court ruled that Bhullar's death sentence could not be commuted to a life term on the grounds that the President took too long to decide on his mercy petition. The verdict is expected to impact the cases of 16 other prisoners on death row who have appealed for clemency on similar grounds, including the seven in Tamil Nadu.
The DMK chief has also asked the J Jayalalithaa government in Tamil Nadu to pass a cabinet resolution to save the three men convicted for the assassination of former Prime Minister Rajiv Gandhi in 1991. "Even if criminals escape; no innocent should be punished," Mr Karunanidhi said, reiterating that the DMK's demand that the centre and state governments work together to abolish the death sentence.
Mr Karunanidhi's party, which is in the opposition in Tamil Nadu, quit the UPA government in March this year.