40-year-old Harkirat was admitted to PGIMER here with a gunshot wound in the head and succumbed this afternoon.
His cousin and Congress MP from Ludhiana, Ravneet Singh Bittu, told reporters that Harkirat was "in depression" for a long time and indicated that he may have committed suicide.
Police said that they are inquiring into the case.
"Harkirat received bullet injury in his head," Sector 3 Police Station's SHO, Neeraj Sarna said.
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"Inquest proceedings under Section 174 of the CrPC (Code Of Criminal Procedure, 1973) are being carried out. Postmortem examination would be carried out tomorrow by a board of doctors either from PGIMER or Govt Hospital at Sector 16 Chandigarh," Sarna said.
Bittu, who reached here from Ludhiana after learning about the incident, said Harkirat, who was the Sarpanch of Kotli village in Ludhiana, had met with an accident some months ago and was not keeping well since.
"In the morning today, he had gone for a walk on the lake. After he returned to the house, he told his wife that he wanted to take a bath.
"Harkirat's wife went inside the kitchen, but within minutes he shot himself," Bittu claimed.
He said that Harkirat's elder brother Gurkirat Singh, Congress MLA from Khanna, was currently abroad while their father and former minister Tej Prakash Singh had gone somewhere locally at the time of the incident.
Harkirat's grandfather Beant Singh was CM of Punjab from 1992 to 1995.
On August 31, 1995, the then Chief Minister, 73-year-old Beant Singh, was killed in a suicide bomb blast at the entrance of the civil secretariat in Chandigarh. 17 others too died in the terror attack by Sikh extremists.
Meanwhile, Punjab Chief Minister Parkash Singh Badal expressed profound grief and sorrow over the demise of Harkirat.
Congress General Secretary in-charge party's Punjab Affairs Shakeel Ahmad and Punjab Congress President Capt Amarinder Singh also condoled Harkirat's death.
Leader of Opposition in Punjab Assembly, Charanjit Singh Channi, also condoled the death of Harkirat Singh.