Born on January 7, 1979 in New Delhi, India, Basu hails from a Bengali family. She is the second of three daughters to her parents, the elder being Bidisha, and the younger—Vijayeta. Although she was born in Delhi, her family later moved to Kolkata.

According to her, she had come into modelling and acting quite by accident, because initially she had planned to study medicine. Basu studied science till the 12th standard at Bhavan's Gangabux Kanoria Vidyamandir and later took up commerce at The Bhawanipur Gujarati Education Society College in Kolkata where she also did modelling and rampshows partime. Although, as pointed above, she intended to become a doctor, her aversion for dissections made her opt for chartered accountancy. However, in 1996, she met well-known model Mehr Jessia in Kolkata; the latter suggested that Basu take part in the Godrej Cinthol Supermodel contest. She eventually participated, and won the contest

After winning the Ford Godrej Cinthol contest, Basu was flown to New York by the Ford Company, where she had a successful modelling career.

Basu made her debut film in Abbas Mustan's Ajnabee, with Akshay Kumar, Bobby Deol and Kareena Kapoor. She played a married woman who goes all out to woo her husband’s married friend, and eventually won the Filmfare Best Female Debut Award for her performance.

After a number film, next year in 2002, Basu starred in Vikram Bhatt's thriller Raaz. The film was a big commercial success and surfaced as the biggest hit of that year. For her performance in the film, she received her first Best Actress nomination at the Filmfare.