Sen was born as Subhamitra Sen in Kolkata, West Bengal. She completed her schooling from Bidya Bharati Girls' High School in 1998. She completed her graduation in Commerce from University of Calcutta.

Since childhood, Sen dreamt of becoming an actress. After completing her studies, she persuaded her mother to accompany her to Mumbai. She later said that she wasn't encouraged by anyone in her family except from her grandfather. After doing the rounds, she got into ads including one Coca-Cola ad with Aamir Khan. She was instantly noticed, and her first offers for films started rolling in.

Sen made her debut as a lead actress in the Telugu movie Nee Thodu Kavali. Her debut Hindi film, Vijay Galani's Hungama was released in 2003. It was a comedy film, in which she co-starred with Akshaye Khanna, Aftab Shivdasani, and Paresh Rawal.

She followed it with appearances in big budget movies like Dhoom (2004), Kyon Ki (2005), Garam Masala (2005) and Golmaal (2006). Sen also did a cameo in the 2006 film Dhoom 2, and she followed it with Johnny Gaddaar alongside newcomer actor Neil Nitin Mukesh. In 2008, she appeared in De Taali and in 2009, Sankat City and Horn Ok Pleasse. All three of these films were box office disasters. After these films, her career declined.

She further appeared in the films Thank you and Shagird in 2011 and both the films were box office failures.

Sen has produced a film Budhia Singh - Born to Run. She changed her screen name, Rimi, to her real name, Subhamitra Sen for her production venture.^[5]

Sen was a celebrity contestant in the ninth season of the Indian version of the reality TV show Big Brother, Bigg Boss.^[6] It went aired in October 2015.^[7] Sen entered the house with Suyyash Rai as her partner for the show; however, her pairing was revised on Day 5 where Rochelle Maria Rao was chosen as her new partner. She was evicted after staying in the house for 7.5 weeks.

Rimi Sen joined BJP in January 2017.