He was 82.
Congress leader Virendra Sharma told PTI that Jagjit Singh began to sweat and complained of chest pain around 5 AM following which he was taken to a private hospital where he passed away.
He is survived by his wife, two sons and two daughters.
Jagjit, a prominent Dalit leader, became an MLA for the first time in 1980.
A five-time party MLA, he was Local Bodies minister in Captain Amarinder Singh's government between 2002 to 2007. He was also leader of the opposition in Punjab Assembly once.