She is born as Revathy to a Chennai settled Malayali family. Her father Ajith is an employee of IOB and her mother Maya is a beautician. She has an elder brother, Rahul. She did her primary education at Vidyodaya Girls Higher Secondary School, Chennai. She did her schooling till Class 9.

She married a Chennai-based IT professional, Venkat Chandrasekharan, on 6 December 2015. The ceremony was held at Guruvayur Temple because of the floods in Chennai.
Now as the couple have done decided to come back Chennai, Sandhya has said, “We had decided to have our wedding and reception, both in a grand manner.But now with the Chennai and people in flood affected areas suffering from the natural disaster, we have decided to donate the money saved by me for the wedding towards the Chennai Flood relief fund”. The couple were blessed with a girl Shaema Venkat on September 2016.

Sandhya was studying when she starred in the critically acclaimed Tamil love story Kaadhal. Initially, this role was offered to actress Gopika, however, due to date problems, this role went on to Sandhya. However, due to her rising fame, especially after the blockbuster film Dishyum, her second Tamil film, she had to discontinue her studies before even passing her 10th class.

After Kaadhal, for which she won the Filmfare Best Tamil Actress Award of 2004, she took up a Malayalam film titled Alice in Wonderland which she played as the sister of actor Jayaram. Then came the musical romance Dishyum with Jeeva. She was also a part of Mani Ratnam's stage show, Netru, Indru, Naalai and many other stage shows. In her third Tamil film, Vallavan, she had only a small role, and the film had only modest box office success. She also acted in Koodal Nagar with Bharath. She debuted in playback singing for her Tamil film Manjal Veiyil.^[4] In 2010, she received a role opposite Vishnuvardhan in the Kannada film Aptharakshaka directed by P. Vasu, her role was very much appreciated by the critics and gave her a very good recognition. The film went on to become a mega hit that run for 35 continuous weeks in the theatres.

She was approached for the voice-over for Shriya Saran's character in Sivaji, however, S. Shankar later preferred actress Kanika Subramaniam's voice.

She has signed Tarun Gopi's forthcoming film Soodhaatam,^[5] Second Innings^[6] and Long Sight.^[7] She has done many dance programmes on different stages.She learnt music in her childhood.She has judged popular reality shows like COMEDY STARS,LITTLE STARS both on Asianet.She has participated in many game shows also.