Congress leader and spokesperson Rajiv Tyagi passed away on Wednesday after a heart attack, the party said. He was 52.
Tyagi suffered the attack soon after participating in a TV debate from his residence in Sector 16 of Vasundhara in Ghaziabad and fell unconscious, sources said.
He was immediately rushed to the Yashoda Hospital in Kaushambi, Ghaziabad, where doctors tried to revive him, but could not, the sources added.
Doctors said he probably breathed his last on the way to the hospital.
Tyagi was a regular Congress face in TV debates and his last tweet came around 3.40 pm Wednesday in which he said he was scheduled to take part in a debate at 5 pm.
After finishing the debate, Tyagi asked his domestic help to prepare tea for him and himself lay down on his bed, his family members said.
But when the house help brought the tea after a few minutes, he did not respond, they said.
His brother-in-law Deepak Tyagi said that a nearby doctor was called for an emergency check-up, but after efforts to revive him failed, Tyagi was immediately rushed to the Yashoda hospital, where the doctors declared him "brought dead".
Tyagi is survived by his wife and two sons.
A host of Congress and Bharatiya Janata Party leaders, besides Union ministers Gajendra Singh Shekhawat and Ram Vilas Paswan expressed their condolences to the family.
Congress president Sonia Gandhi, and party leaders Rahul Gandhi and Priyanka Gandhi Vadra spoke to Tyagi's wife on phone and expressed their condolences while remembering his contribution to the party.
The Congress tweeted, "We are deeply saddened by the sudden demise of Shri Rajiv Tyagi. A staunch Congressman and a true patriot. Our thoughts and prayers are with his family and friends in this time of grief."
In his condolence message, Rahul Gandhi said the Congress "lost one of its lions today".
"The inspiration of Rajiv Tyagi's love and struggle for the Congress will always be remembered. My heartfelt tribute to him and condolences to the family," he tweeted in Hindi.
In her tweet, Priyanka Gandhi said Tyagi's untimely demise is a big loss for all.
"The untimely death of Congress spokesman Rajiv Tyagi is a personal grief to me. It is an irreparable loss for all of us. Rajiv ji was an ideologically dedicated warrior. I expressed condolences to his family on behalf of the entire Uttar Pradesh Congress. May God give strength to his family to bear this loss," she said.
Leader of Opposition in Rajya Sabha Ghulam Nabi Azad said, "Deeply saddened to hear the shocking news of untimely death of young congress leader & spokesperson Rajiv Tyagi. My heartfelt condolences to the family to bear the irreparable loss."
AICC general secretary KC Venugopal said, "Saddened and shocked to hear about the sudden demise of our colleague and Congress national spokesperson Shri Rajiv Tyagi. My condolences to his family and friends in this time of grief. May his soul rest in peace."
Party chief spokesperson Randeep Surjewala said he was speechless on hearing about Tyagi's demise. He said it is a personal loss for him.
"Saddened to know of untimely demise of INC national spokesperson, Shri Rajiv Tyagi. He served the party dedicatedly. My heartfelt condolences to his family members & friends," tweeted Rajasthan Chief Minister Ashok Gehlot.
Chhattisgarh Chief Minister Bhupesh Baghel said Tyagi's death was an irreparable loss for the party.
BJP MP Anil Baluni, who also heads the party's media department, expressed his shock at the death of Tyagi, saying he was an affable and emotional person.
Several BJP spokespersons, who regularly debated with Tyagi in TV shows, expressed their sorrow at his demise.
BJP spokesperson Sambit Patra, who was on a TV debate with Tyagi just before his death, said, "I cannot believe that my friend Rajiv Tyagi is no more. We were together in a TV debate at 5 pm. Life is very uncertain. I don't have words to express. May God give Rajiv ji a place in his feet."
Tyagi will be cremated on Thursday morning at Hindon crematorium, party sources said.