She had been admitted to AIIMS earlier in the night.
Swaraj, who was external affairs minister in the Narendra Modi government’s first term from 2014 to 2019, had cited health concerns as the reason for not contesting the general election.
She was earlier the opposition leader in the Lok Sabha from 2009 to 2014.
AIIMS has released a statement saying, Swaraj suffered a cardiac arrest, was administered CPR but did not respond.
The news broke just four hours after she posted a tweet thanking Modi for revoking Article 370.
Her tenure as foreign minister is best remembered for her active interventions on Twitter, where ordinary people across party lines reached out to her for help with matters ranging from lost passports to being stranded abroad.
“A glorious chapter in Indian politics comes to an end. India grieves the demise of a remarkable leader who devoted her life to public service and bettering lives of the poor. Sushma Swaraj Ji was one of her kind, who was a source of inspiration for crores of people,” Prime Minister Narendra Modi tweeted.
The former Union minister is survived by her husband Swaraj Kaushal and daughter Bansuri.
Swaraj’s mortal remains were taken to her Delhi residence. Her mortal remains will be kept from 12pm-3pm at the BJP headquarters on Wednesday for party workers and leaders to pay tributes, BJP working president JP Nadda said. Her last rites will be performed at the Lodhi crematorium, he said.
Swaraj started her political life with the Akhil Bharatiya Vidyarthi Parishad, the RSS’ student wing, and later joined the BJP.
She was the Information and Broadcasting Minister in the 13-day Atal Bihari Vajpayee government in 1996 and got the Cabinet portfolio again after he led the BJP to power in 1998.
Long seen as a protege of veteran BJP leader L K Advani, she also was the Leader of the Opposition in the Lok Sabha between 2009-14.
Swaraj, a law graduate who practised in the Supreme Court, was elected seven times as a member of Parliament and three times as a member of the legislative assembly.
Swaraj was external affairs minister from 2014 to 2019, leader of the Opposition in the Lok Sabha from 2009 to 2014, minister for information and broadcasting in Vajpayee government from 2000-2003.