Sandhya was born as Revathi in Alwaye, Kerala on 27th September 1989. Sandhya was two years old when her family moved to Chennai, Tamil Nadu. Her mother Maya Ajith Kumar is a beautician and father Ajith Kumar is a cashier at the National bank. Sandhya has an elder brother Rahul who studies at SRM College, Chennai. The actress finished her schooling from Vidyodaya School and planned to go for a course in Visual Communications. But she couldn't complete her tenth standard examinations and had to discontinue her studies.
Director Balaji Sakthive discovered her and soon she found herself playing the lead role in Kaadhal (2004) as Aishwarya opposite actor Bharath. It is a story about a convent school girl who loves Murugan, a motor mechanic. Her acting in this movie was outstanding and she also received an award for the Best Filmfare Actress (South) in 2004. After this movie she was also named as Kutty Kajol.
The actress became more prominent after the success of Sasi's Dishyum. This movie was a superhit and starred actor Jeeva. It was a cute love story. Sandhya played a minor role in the Tamil movie Vallavan. She has participated Mani Ratnam's stage show, Netru, Indru, Naalai.
In the Malayalam movie Alice in Wonderland she played the lead role of Alice with actor Jayaram who appeared as Alby. Her most recent release was the Tamil movie Mahesh Saranya Matrum Palar (2008) which is about Mahesh (Sakthi) who is excited to get married and wants his sister to get married as soon as possible, but there are various hurdles in his way.
M.Raja's Manjal Veyyil was one of her releases in 2009, in which she was paired with actor Prasanna. Her fans can see her in Irumbu Kottai Murattu Singam and Haasini in 2010.