Since childhood Sen nursed the dream 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 for 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 offer for films started rolling in.
Rimi made her debut as a lead actress in Telugu movie Nee Thodu Kavali. Her debut Hindi film, Vijay Galani's Hungama, released in 2003. It was a comedy film, in which she co-starred with Akshaye Khanna, Aftab Shivdasani, Paresh Rawal, as well as other actors.