Basu was born on 7 January 1979 in New Delhi to a Bengali Hindu family. She is the middle child of three daughters: she has an elder sister named Bidisha and a younger named Vijayeta. Basu's family later moved to Kolkata shortly before she entered middle school.
In an interview, she has stated that she had initially planned to study medicine, but entered modelling and acting by accident Basu studied science till the 12th standard at Bhavan's Gangabux Kanoria Vidyamandir and then studied commerce at The Bhawanipur Gujarati Education Society College, an undergraduate college affiliated with the University of Calcutta. In Kolkata, she did modelling and ramp shows part-time.When she was 17, she met model Mehr Jessia in Kolkata; the latter suggested that Basu take part in the Godrej Cinthol Supermodel contest. Basu participated, and eventually won the contest.