Veteran politician and former Janata Dal-United chief Sharad Yadav died on Thursday at a private hospital in Gurugram, family sources said. He was 75.
He is survived by his wife, a daughter and a son.
A statement from the Fortis Memorial Research Institute said Yadav was brought to the emergency ward in an unconscious and unresponsive state.
"On examination, he did not have any pulse or recordable blood pressure. He underwent CPR as per ACLS protocols. Despite best efforts, he could not be revived and was declared dead at 10.19 pm," the statement said.
Yadav's associates said he collapsed at his Chhatarpur residence on Thursday night and was taken to Fortis hospital in Gurugram but could not be saved.
The veteran socialist leader had been suffering from kidney-related issues for a long time and regularly underwent dialysis.
Prime Minister Narendra Modi expressed condolences over Yadav's demise.
"Pained by the passing away of Shri Sharad Yadav Ji. In his long years in public life, he distinguished himself as MP and minister. He was greatly inspired by Dr. Lohia's ideals. I will always cherish our interactions. Condolences to his family and admirers. Om Shanti," he tweeted.
Congress president Mallikarjun Kharge condoled Yadav's demise and said he strengthened the politics of quality.
The Congress also said Yadav's demise is an irreparable loss to Indian politics.
Bihar deputy Chief Minister Tejashwi Yadav also expressed grief on Yadav's demise.
"I am saddened by the news of the untimely demise of Mandal Messiah...great socialist leader and my guardian respected Sharad Yadav ji. I am speechless," he tweeted in Hindi.
The RJD leader said he had a conversation with his family members.
"In this hour of grief, the entire Samajwadi fraternity is with his family members," he said.