Reema Sen was born in Kolkata on 29 October 1981. She completed high school from St Thomas Girls School in Kidderpore, Kolkata, after which her family moved to Mumbai. Reema Sen married businessman Shiv Karan Singh in 2012. She gave birth to her first child, a boy named Rudraveer, on 22 February 2013.
In Mumbai, she began her modelling career, appearing in a number of advertising campaigns. She then moved to acting with a block-buster Telugu film Chitram, in which she acted opposite Uday Kiran. She also appeared in the Tamil film, Minnale, which was very successful. Her first Hindi film Hum Ho Gaye Aapke flopped, and she decided to continue working in Tamil cinema. Her appearance in the Tamil film, Rendu, was successful. People found her facial expressions in the film Thimiru endearing and her performance in Vallavan was applauded. Her role in Aayirathil Oruvan was highly praised by viewers and critics.
In April 2006, a Madurai court issued non-bailable warrants against Sen and Shilpa Shetty for "posing in an obscene manner" in photographs published by the Tamil newspaper Dinakaran, owned by Sun Group. The report stated that the two actresses had failed to comply with earlier summons for the same reason, hence the issuance of the warrants. The petitioner submitted that the paper had published "very sexy blow-ups and medium blow-ups" in its December 2005 and January 2006 issues, and which allegedly violated the Indecent Representation of Women (Prohibition) Act 1986, Young Persons (Harmful Publications) Act 1956, and the Indian Penal Code Section 292 (Sale of Obscene Books). The petitioner further demanded that the images should be confiscated under the terms of the Press and Registration of Book Act 1867.