Nandy was born in a Bengali Christian family at Bhagalpur, Bihar, in 1937. He is the eldest of three sons of Satish Chandra Nandy and Prafulla Nalini Nandy, and brother of Pritish Nandy. Later, his family moved to Calcutta. Nandy's mother was a teacher at La Martiniere School, Calcutta and subsequently became the school's first Indian vice principal. When he was 10, British India was partitioned into two sovereign countries – India and Pakistan. He witnessed the time of conflicts and atrocities that followed.