Mahathi started singing for commercial albums from her school days and has sung a in a lot of Malayalam devotional albums.
Mahathi did her schooling at Chinmaya Vidyalaya and Hari Sri Vidya Nidhi in Thrissur, and later continued at Sacred Heart Convent in Kochi.
At this juncture, during one of her visits to Chennai, she had the opportunity of meeting Isai Gnani IIayaraja. The Isai Gnani, recognising her musical talents, made her sing a solo song Enna Maranthalum in the movie Kaadhal Jaathi, for which he composed music.
The year 2003 was a turning point in Mahathi's life. On May 1 2003 her smash hit Aiyyaiyyo Pudichirukku, a duet song with Sri Hariharan, for Vikram's super hit movie Saamy, with Sri Harris Jeyaraj scoring the music.
She has sung more than 700 songs in many languages – like Tamil, Telugu, Kannada, Malayalam and Punjabi.
She has performed all around the world including famous venues like the Sydney Opera House. She has sung performed with Late. Sri T M Soundararajan, Dr K J Yesudas, Sri S P Balasubramaniam, Sri Hariharan, Smt P Susheela, Smt S Janaki, Sri Mano, Smt K S Chitra and many others.
Mahathi received the prestigious Tamil Nadu Government State Award for the Best Playback Singer in 2008 for her song Nera Varattuma from Nenjathai Killadhey.
Mahathi has sung for a lot of jingles for commercial advertisements for Pothys, The Chennai Silks, Khazana Jewellery, Sathya Home Appliances, AVR Swarna Mahal, Achi Masala and many others.
She has rendered title songs for serials like Sahana, Priyamudan KB, Rekkai Kattiya Manasu, Ethirneechal and Makkal Arangam.
She has anchored the show Aha Paadalam in Doordarshan Pothigai.
She was invited by Maestro Ilaiyaraja to anchor the show Andrum Indrum Endrum Maestro, the first ever live–in concert of Isiagnani Ilayaraja at the Indoor Stadium Chennai.
In 2013, she performed Fusion concerts in the UK and Canada with Sri Rajesh Vaidhya, Famous Veena Player and Stephen Devassy, renowned pianist and many other famous musicians.
She has been working with leading music directors like Isaignani Ilayaraja, A R Rahman, Harris Jeyaraj, Yuvan Shankar Raja, Karthik Raja, D Imman, Bharadwaj, Thaman, Vijay Ebenezer, Joshua Sridhar and many others.