Riya, who hails from a family of actors including her grandmother Suchitra Sen, mother Moon Moon Sen and sister Raima Sen, began her acting career in 1991 as a child artiste in the film Vishkanya. Her first commercial success in her film career was with Style, a 2001 Hindi low-budget sex comedy directed by N. Chandra. Some of her other films include producer Pritish Nandy's musical film, Jhankaar Beats (2001) in Hinglish, director David Dhawan's comedy film, Shaadi No. 1 (2005) and director-cinematographer Santhosh Sivan's Malayalam horror film Ananthabhadram (2005).
Riya was first recognised as a model when she performed in Falguni Pathak's music video Yaad Piya Ki Aane Lagi at the age of sixteen. Since then, she has appeared in music videos, television commercials, fashion shows, and on magazine covers.
Riya has worked as an activist and appeared in an AIDS awareness music video with the aim of dispelling popular myths about the disease. She also helped raise funds for pediatric eye-care. Riya has faced controversies such as a MMS clip with actor Ashmit Patel, her semi-nude photograph on photographer Dabboo Ratnani's annual calendar and her on-screen kisses in a conservative Indian film industry.