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 in 1998. 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 first appeared as a child artist in the film Vishkanya in 1991, where she played the role of the young Pooja Bedi. At the age of 19, she did National Film Awards winning director Bharathiraja's Tamil film, Taj Mahal (2000), which did not achieve commercial success. She was scheduled to make her Bollywood film debut in Love You Hamesha, opposite actor Akshaye Khanna; however, the film was stalled, and she finally made her debut in N. Chandra's Style in 2001. This low-budget sex comedy was the first commercial success in over a decade for the director. A launch pad for Riya, cast in the female lead along with fellow-newcomers, Sharman Joshi, Sahil Khan and Shilpi Mudgal, the film pioneered a trend of commercial success for small budget films in India. Riya and the second female lead of the film were replaced by aspirant actresses Sonali Joshi and Jaya Seal in Xcuse Me'.
Her next success was Jhankaar Beats, a comedy revolving around the music of legendary composer R D Burman, which saw her playing a small and glamorous role alongside Shayan Munshi, Juhi Chawla, Rahul Bose, Rinke Khanna and Sanjay Suri. Produced by Pritish Nandy, publishing director of The Times of India, the film was made on a budget of Rs. 25 million (US$525,000), marking the sixth in a row of small to medium budget films made by Pritish Nandy Communications (PNC). Despite being part of a wave of offbeat films that mostly failed to make an impact at the box office, it drew public attention upon its release, which led to a commercial success among a restricted audience targeted by a selective release in twenty cities. It was one of the first films made in Hinglish, a mixture of Hindi and English. In 2005, she starred in Shaadi No. 1, which had no female lead. This comedy, based on the theme of modern marriage, was directed by David Dhawan, a renowned film director from this genre.
Although films like Style and Jhankar Beats succeeded commercially, most of her later films have generated less revenue. A number of them remained unfinished. While many of her appearances have been item numbers and cameos, few of her leading roles have been in low-budget films. Though she had small roles in Dil Vil Pyar Vyar (2002), Qayamat (2003) and Plan (2004), attention was drawn to her item numbers in all three, especially the one in Qayamat that featured her in a bubble-bath. Besides this, she performed another item number in James (2005) on director-producer Ram Gopal Varma's behest, who has a history of casting aspirant actress-models like Sameera Reddy, Isha Koppikar and Koena Mitra in similar roles. Furthermore, she took part in a dance number for Sajid Khan's Heyy Babyy (2007) that featured several mainstream Bollywood actresses.
Riya has, in addition to Hindi films, appeared in Bengali, Tamil, Telugu, Malayalam and English films. Her film career began in the earnest with Tamil films such as Bharathi Raja's Taj Mahal, co-starring Manjoj Bharatiraja in the male lead, and Manoj Bhatnaghar's Good Luck, opposite Prasanth. Both of the films failed commercially, and she had a brief reappearance in Tamil cinema only to perform in a dance number for N. Maharajan's Arasatchi.
Her first English language movie was It Was Raining That Night, a remake of the Bengali film Hei Brishtir Raat, scripted by Sudeshna Roy and directed by Mahesh Manjrekar. In the film, she collaborated with mother Moon Moon Sen. Riya was slated to appear in Anjan Dutt's Bengali-English bilingual film The Bong Connection with her sister, but she was eventually dropped from the project and replaced by Peeya Rai Chaudhary. The two sisters were later cast together in director Ajai Sinha's The Bachelor, a Bengali film that, as of 2008, is yet to be finished.
Her most successful non-Hindi film has been director Santhosh Sivan's Ananthabhadram (2005). The first Malayalam venture for both Riya and Sivan, was both a critical and commercial success. It won five Kerala State Film Awards and surfaced as one of the biggest Malayalam successes that year. She played the role of Bhama in the film, a village girl who is lured by Digambaran, the evil magician portrayed by Manoj K. Jayan. In a song-and-dance sequence showing Digambaran turning Bhama into a medium for demonic rituals, the choreographer Aparna Sindoor made abundant use Kathakali movements. The use of Kathakali has been a high point in the resurgence of the classical dance form in other major Indian films as well, including Shaji Karun's Vanaprastham (1999) and Adoor Gopalakrishnan's Kalamandalam Ramankutty Nair (2005). She made her Telugu Debut with Nenu Meeku Telusa...?, in which she was paired opposite Manoj Manchu.
In 2012 Sen won the Star Guide Award as best actress for her performance in Noukadubi.
Riya became a popular model when she appeared in numerous music videos for songs by popular singers, including Falguni Pathak's Yaad Piya Ki Aane Lagi (alternative title: Chudi Jo Khankayi), Asha Bhosle's Jhumka Gira Re, Jagjit Singh and Bhosle's Jab Samne Tum and Kahin Kahin Se, Lata Mangeshkar, Bhonsle and Singh's Dil Kahin Hosh Kahin, Sonu Nigam's Jeena Hai Tere Liye and Shaan's Sutta Maro. She shot for her first music video, Yaad Piya Ki Aane Lagi, at the age of sixteen. This led to her being identified primarily as a performer for music videos early in her career, an image she aimed to shed in 2005. Riya has appeared on several magazine covers, including Femina, Elaan, Man's World, Gladrags, Savvy and Indian versions of Elle, Maxim and Cosmopolitan, as well as on the ramp of major fashion shows like Lakmé Fashion Week (2005–07) and Wills Fashion Week (2006–2007). She participated in fashion shows along with her elder sister, Raima Sen. Besides modelling, Riya has ventured into the advertisement world as well. A high point of her modelling career came in 2006, when she became the soft drink, Limca's brand ambassador, replacing Deepika Padukone. Her other notable assignments include Colgate, Dabur Vatika, Reliance Industries, Cadbury Dairy Milk Chocolate, and Nirma.
In 2004, she was featured partially nude in leading Indian photographer Dabboo Ratnani's annual calendar, which is a major happening in the Indian glamour industry. According to Daboo, "Her mother saw it much later, after the calendar released. She thought it was too sexy, and Riya shouldn't have done it. But the response to the photograph was superb. Riya was so thrilled that for her next ad campaign, she asked me to light her up like I did in this." A career highlight for the model, it led to a three-year contract with Ratnani to feature her on his annual calendar. She is the only female face to be featured on the calendar for five consecutive years (2003–07).
Born on 24 January 1981 in Kolkata, West Bengal, Riya is the daughter of Moon Moon Sen, a former actress, and granddaughter of Suchitra Sen, a legend in Bengali cinema. Before leaving for Mumbai, she lived in Kolkata with her parents and sister Raima Sen, also an actress. Her father Bharat Dev Varma is a member of the royal family of Tripura. Her paternal grandmother, Ila Devi, was the princess of Cooch Behar, whose younger sister Gayatri Devi was the Maharani of Jaipur. Her paternal great-grandmother Indira was the only daughter of Maharaja Sayajirao Gaekwad III of Baroda. Riya's maternal great-grandfather Adinath Sen was a prominent Kolkata businessman, whose father Dinanath Sen – a relative of former Union Law Minister Ashoke Kumar Sen- was the Diwan or a Minister of the Maharaja of Tripura. The sisters are credited on-screen under their mother's maiden name, although their official papers carry the surname Dev Varma.
Riya completed her schooling at Loreto House and Rani Birla Girls' College (a University of Calcutta affiliate), both in Kolkata. Thereafter, she studied at the National Institute of Fashion Technology, and she took up jewellery-designing as a hobby. She designs most of the clothes that she wears in films and commercials. Riya is trained in Kathak and is still pursuing it under Vijayshree Chaudhury. She is taking kickboxing lessons and has completed Level I of the 5 levels in belly dancing. Riya entered the film industry through small-time modelling assignments, commuting between Mumbai and Kolkata and travelling by public transport during her early career. After breaking into the film industry, she shifted from her mother's house in Ballygunge Circular Road in south Kolkata to Mumbai. There she moved into the family house in Juhu, where she stays with her sister.
Riya has suffered a number of untimely incidents. During the filming of Shaadi No. 1 in France, she was knocked unconscious after being accidentally run over by a stuntman's motorbike, but she was not seriously injured. Shortly before the release of Silsiilay, in which she starred opposite her boyfriend Ashmit Patel, a 90-second video clip was circulated on Multimedia Messaging Services and the internet, showing the pair in compromising situations in a hotel bedroom. This was one of a number of controversies that erupted when celebrities were caught in similar situations using cameraphones. Following this incident, the couple split up, although Riya denied that she was the girl in the MMS clip. One commentator claimed that the footage was an orchestrated publicity stunt. In 2007, she underwent a brief detoxification period in Bangkok for addiction to chocolate.
In August 2017, Sen married her boyfriend Shivam Tewari in a private Bengali Hindu ceremony.
Riya's on-screen performances have established her as a bold youth icon in India. Since entering the film industry, she has gained attention for wearing a bikini in Shaadi No. 1 and sharing on-screen kisses with co-stars Ashmit Patel in Silsiilay and Sharman Joshi in Style, respectively. Such performances garnered negative attention because of the relatively conservative outlook of Indian cinema at that time and her own statements about such practices. In 2008, Riya Sen was also linked to author Salman Rushdie. Before becoming a film star, she had a reputation for partying, which started at the age of fifteen. Riya's public persona is compared to her mother Moon Moon, who was seen as a sex symbol of her time, while her sister Raima is mostly compared to their grandmother Suchitra.
Although her film career has yet to achieve large-scale success, Riya has generated considerable media attention. She was ranked ninth on Femina 50 Most Beautiful Women, published in the magazine's September 2007 issue. She was a jury member for the 2008 Final of the Mr. India contest. Riya appeared in Haath Se Haath Mila, an HIV/AIDS awareness music video. She made charity appearances at McDonald's India to raise money for paediatric eye-care during World Children's Week (14–20 November) in 2003.