Mahathi is a Carnatic musican and playback singer for film songs in several Indian languages. She was born in Chennai to a family of Carnatic musicians. Her maternal great grandfather, Pazhamaneri Swaminatha Iyer, was a Carnatic vocalist and recipient of the Sangeetha Kalanidhi title. Her mother, Vasanthi Sekhar, was a flautist, while her father, Thiruvaiyaru Sekar was a Carnatic vocalist and disciple of M. Balamuralikrishna. She moved to Kerala as a toddler, and did her schooling Hari Sri Vidya Nidhi, Trichur and Sacred Heart Convent, Cochin. She graduated in Chennai from Meenakshi College, Kodambakkam with English literature as her main stream. She was married on 16 March 2008 to Dr. K. Sreekumar, an oral and maxillo facial surgeon. Their son, Samarth, was born on 27 February 2011.
She is a famous vocalist and playback singer of Tamil movies. She is an 'A Grade' artiste (Carnatic Classical Vocal) of All India Radio. She has also sung for many television commercials and serials. A few of her noted Tamil hits include Aiyyayo Aiyyayo Pidichirukku of Samy, Kaadhalikkum of Chellamae, Nenjae Nenjae of Ayan, Mudhal Mazhai of Bhima and Innisai of Varalaru. She has been given top songs by music director Harris Jayaraj and Aiyyayo Aiyyayo Pidichirukku of Samy and Mudhal Mazhai of Bhima needs special mention. Both songs were pictured on Vikram and Trisha and her co-singer being Hariharan. She received scholarships from Indian government in 1994 and has also done many devotional albums from Thrissur. She started live concerts at the age of 10.