Indian media reported that Sunil breathed his last at his residence in Kolkata around 2am and that he was suffering from various ailments for quite a while.
His family friend Dipendu Bhattacharya said he was not keeping well of late. "He was supposed to go to the doctor. But he said he would go later. We had a long conversation at night… he (Sunil) went to the bathroom and after several minutes he had a heart attack."
The news of his death came as a big shock for the literature and cultural spheres in both West Bengal and Bangladesh. Many rushed to his Kolkata home to see this celebrated writer for one last time.
Sunil's mortal remains were taken to the Peace Haven mortuary in the morning. Indian TV station ETV Bangla reported that Sunil's funeral would take place in Kolkata on Wednesday.
Well-known author Amitav Ghosh wrote on the micro-blogging site Twitter: "Deeply shocked by the death of the great Bengali writer Sunil Gangopadhyay. He was warm, kind man and a dear friend. Will miss him terribly."
News agency Press Trust of India quoted Shirshendu Mukhopadhyay, condoling his death, as saying, "It will be extremely difficult to fill the vacuum in Bengali literature after his death as Sunil had heralded a new style in Bengali literature".
Sunil – a poet, novelist, short-story writer, journalist and columnist – was born in Bangladesh's Faridpur district on Sep 7, 1934. He left for Kolkata along with his family at the age of four and did his masters from Kolkata University in 1954.
He came to Bangladesh on several occasions to attend programmes and on personal visits and shared a friendly relation with one of Bangladesh's most celebrated writers Humayun Ahmed, who also died recently. Sunil would hang out with Humatun at Gazipur's Nuhash Palli retreat built by latter.
Bangladesh's War of Independence in 1971 had stirred Sunil's young mind. He visited the refugee camps in India on several occasions and wrote for the people from his birthplace.
A year before finishing his studies, Sunil started editing a publication on poetry, Krittibash. His first poetry collection, 'Eka O Koyekjon', hit the stands in 1958 and his first novel, 'Atmaprakash' followed after eight years.
Sunil was one of the activists of Hungryalist literary movement in India. Poems from his 'Nikhilesh' and 'Neera' series were popular among the youth for a long time.
Nearly eight years after publication of his first book of poems, his maiden novel 'Atmaprakash' was published in 1966.
Sunil also wrote under the pen names Nillohit, Shonatan Pathok, Nil Upaddhyay. He also held offices as presidents of India's national literary organisations Sahitya Akademy and the Paschimbanga Shishu Kishore Academy.
His mentionable works are 'Ami kirokombhabe beche achhi', 'Jugalbandi', 'Hotat Nirar Jonnye', 'Ordhek Jibon', 'Arannyar Din Ratri', 'Prothom Alo', 'Shei Shomoy', 'Purba Poshchim' and 'Moner Manush'.
Leading Indian columnist Anurag Mazumdar in a tribute said: "For some, he was also the man who brought modern Bengali literature to its brush with history – with a tome like Purba Paschim. The writer had taken that ardous journey of a refugee like several people during the Partition.
"The two-volume book depicting the multiple images of the Bengal partition through the eyes of several people in Bengal, Bangladesh and elsewhere took Bengali literature to its nadir in historical fiction. It remains to this day a landmark in Bengali literature."
Film maestro Satyajit Ray made films based on Sunil's Arannyar Din Ratri, 'Pratidhwani and 'Arjun', while Gautam Ghosh adapted for the screen his novel on Fakir Lalon Shah, Moner Manush. Other film-makers have adapted many of his works.
He was awarded the Ananda Puroshkar two times in 1972 and 1989, Sahitya Akademy Puroshkar in 1985, and The Hindu Literary Award in 2011 for his contributions in the literary arena.
His friends in Kolkata could not even think that he would leave so early.
Shirshendu Mukhopadhyay, himself a popular writer and a friend of Sunil, told an Indian TV channel that everyone knew how big a literary person Sunil was but not everyone would know how big-hearted a man he was.
"A man, so soft hearted, emotional and gentle is rarely seen. I know how many people he had helped out secretly," he added.
Sunil had taken up journalism as his profession. He had worked for a long time for India's one of the largest circulated Bengali-language dailies, Dainik Anandabazar.
The West Bengal government in 2002 honoured this legendary writer by appointing him as honourary 'Sheriff of Kolkata'.
Sunil married Swati Bandopaddhyay in 1967 and fathered one son, Shouvik Gangopadhyay.
